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Some examples of this type of differential equation are dx dy +x = cos y 2 dx x dy +−y = y2e – y To solve the first order linear differential equation of the type P dy y dx = Q (1) Multiply both sides of the equation by a function of x say g (x) to get g(x) dy dx + P (g(x)) y = Q g (x)
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(1) Multiply both sides of the equation by a function of x say g (x) to get g(x) dy dx + P (g(x)) y = Q g (x) (2) © NCERT not to be republished MATHEMATICS 408 Choose g (x) in such a way that R
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(g(x)) y = Q g (x) (2) © NCERT not to be republished MATHEMATICS 408 Choose g (x) in such a way that R H
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4821-4824
g (x) (2) © NCERT not to be republished MATHEMATICS 408 Choose g (x) in such a way that R H S
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4822-4825
(2) © NCERT not to be republished MATHEMATICS 408 Choose g (x) in such a way that R H S becomes a derivative of y
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4823-4826
H S becomes a derivative of y g (x)
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4824-4827
S becomes a derivative of y g (x) i
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4825-4828
becomes a derivative of y g (x) i e
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4826-4829
g (x) i e g(x) dy dx + P
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4827-4830
i e g(x) dy dx + P g(x) y = d dx [y
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4828-4831
e g(x) dy dx + P g(x) y = d dx [y g (x)] or g(x) dy dx + P
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4829-4832
g(x) dy dx + P g(x) y = d dx [y g (x)] or g(x) dy dx + P g(x) y = g(x) dy dx + y g′ (x) ⇒ P
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4830-4833
g(x) y = d dx [y g (x)] or g(x) dy dx + P g(x) y = g(x) dy dx + y g′ (x) ⇒ P g(x) = g′ (x) or P = ( ) ( ) g x g x ′ Integrating both sides with respect to x, we get ∫Pdx = ( ) ( ) g x dx ′g x ∫ or P dx ∫⋅ = log(g (x)) or g(x) = P dx e∫ On multiplying the equation (1) by g(x) = e∫P dx , the L
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4831-4834
g (x)] or g(x) dy dx + P g(x) y = g(x) dy dx + y g′ (x) ⇒ P g(x) = g′ (x) or P = ( ) ( ) g x g x ′ Integrating both sides with respect to x, we get ∫Pdx = ( ) ( ) g x dx ′g x ∫ or P dx ∫⋅ = log(g (x)) or g(x) = P dx e∫ On multiplying the equation (1) by g(x) = e∫P dx , the L H
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4832-4835
g(x) y = g(x) dy dx + y g′ (x) ⇒ P g(x) = g′ (x) or P = ( ) ( ) g x g x ′ Integrating both sides with respect to x, we get ∫Pdx = ( ) ( ) g x dx ′g x ∫ or P dx ∫⋅ = log(g (x)) or g(x) = P dx e∫ On multiplying the equation (1) by g(x) = e∫P dx , the L H S
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4833-4836
g(x) = g′ (x) or P = ( ) ( ) g x g x ′ Integrating both sides with respect to x, we get ∫Pdx = ( ) ( ) g x dx ′g x ∫ or P dx ∫⋅ = log(g (x)) or g(x) = P dx e∫ On multiplying the equation (1) by g(x) = e∫P dx , the L H S becomes the derivative of some function of x and y
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4834-4837
H S becomes the derivative of some function of x and y This function g(x) = e∫P dx is called Integrating Factor (I
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4835-4838
S becomes the derivative of some function of x and y This function g(x) = e∫P dx is called Integrating Factor (I F
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4836-4839
becomes the derivative of some function of x and y This function g(x) = e∫P dx is called Integrating Factor (I F ) of the given differential equation
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4837-4840
This function g(x) = e∫P dx is called Integrating Factor (I F ) of the given differential equation Substituting the value of g (x) in equation (2), we get P P P dx dx dy e e y dx = P Q e dx or Pdx d dxy e = P Q dx e Integrating both sides with respect to x, we get y e Pdx = P Q dx e dx or y = P P Q C dx dx e e dx which is the general solution of the differential equation
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4838-4841
F ) of the given differential equation Substituting the value of g (x) in equation (2), we get P P P dx dx dy e e y dx = P Q e dx or Pdx d dxy e = P Q dx e Integrating both sides with respect to x, we get y e Pdx = P Q dx e dx or y = P P Q C dx dx e e dx which is the general solution of the differential equation © NCERT not to be republished DIFFERENTIAL EQUATIONS 409 Steps involved to solve first order linear differential equation: (i) Write the given differential equation in the form P Q dy dx +y = where P, Q are constants or functions of x only
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4839-4842
) of the given differential equation Substituting the value of g (x) in equation (2), we get P P P dx dx dy e e y dx = P Q e dx or Pdx d dxy e = P Q dx e Integrating both sides with respect to x, we get y e Pdx = P Q dx e dx or y = P P Q C dx dx e e dx which is the general solution of the differential equation © NCERT not to be republished DIFFERENTIAL EQUATIONS 409 Steps involved to solve first order linear differential equation: (i) Write the given differential equation in the form P Q dy dx +y = where P, Q are constants or functions of x only (ii) Find the Integrating Factor (I
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4840-4843
Substituting the value of g (x) in equation (2), we get P P P dx dx dy e e y dx = P Q e dx or Pdx d dxy e = P Q dx e Integrating both sides with respect to x, we get y e Pdx = P Q dx e dx or y = P P Q C dx dx e e dx which is the general solution of the differential equation © NCERT not to be republished DIFFERENTIAL EQUATIONS 409 Steps involved to solve first order linear differential equation: (i) Write the given differential equation in the form P Q dy dx +y = where P, Q are constants or functions of x only (ii) Find the Integrating Factor (I F) = ePdx
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4841-4844
© NCERT not to be republished DIFFERENTIAL EQUATIONS 409 Steps involved to solve first order linear differential equation: (i) Write the given differential equation in the form P Q dy dx +y = where P, Q are constants or functions of x only (ii) Find the Integrating Factor (I F) = ePdx (iii) Write the solution of the given differential equation as y (I
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4842-4845
(ii) Find the Integrating Factor (I F) = ePdx (iii) Write the solution of the given differential equation as y (I F) = Q × I
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F) = ePdx (iii) Write the solution of the given differential equation as y (I F) = Q × I F C dx In case, the first order linear differential equation is in the form 1 1 P Q dx x dy + = , where, P1 and Q1 are constants or functions of y only
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4844-4847
(iii) Write the solution of the given differential equation as y (I F) = Q × I F C dx In case, the first order linear differential equation is in the form 1 1 P Q dx x dy + = , where, P1 and Q1 are constants or functions of y only Then I
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4845-4848
F) = Q × I F C dx In case, the first order linear differential equation is in the form 1 1 P Q dx x dy + = , where, P1 and Q1 are constants or functions of y only Then I F = e 1P dy and the solution of the differential equation is given by x
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4846-4849
F C dx In case, the first order linear differential equation is in the form 1 1 P Q dx x dy + = , where, P1 and Q1 are constants or functions of y only Then I F = e 1P dy and the solution of the differential equation is given by x (I
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4847-4850
Then I F = e 1P dy and the solution of the differential equation is given by x (I F) = ( ) 1 Q × I
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4848-4851
F = e 1P dy and the solution of the differential equation is given by x (I F) = ( ) 1 Q × I F dy +C ∫ Example 19 Find the general solution of the differential equation cos dy y x dx − =
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4849-4852
(I F) = ( ) 1 Q × I F dy +C ∫ Example 19 Find the general solution of the differential equation cos dy y x dx − = Solution Given differential equation is of the form P Q dy y dx + = , where P = –1 and Q = cos x Therefore I
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4850-4853
F) = ( ) 1 Q × I F dy +C ∫ Example 19 Find the general solution of the differential equation cos dy y x dx − = Solution Given differential equation is of the form P Q dy y dx + = , where P = –1 and Q = cos x Therefore I F = 1 dx x e e Multiplying both sides of equation by I
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4851-4854
F dy +C ∫ Example 19 Find the general solution of the differential equation cos dy y x dx − = Solution Given differential equation is of the form P Q dy y dx + = , where P = –1 and Q = cos x Therefore I F = 1 dx x e e Multiplying both sides of equation by I F, we get x x dy e e y dx − −− = e–x cos x or ( dy yex) dx − = e–x cos x On integrating both sides with respect to x, we get ye– x = cos C ex x dx − + ∫
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4852-4855
Solution Given differential equation is of the form P Q dy y dx + = , where P = –1 and Q = cos x Therefore I F = 1 dx x e e Multiplying both sides of equation by I F, we get x x dy e e y dx − −− = e–x cos x or ( dy yex) dx − = e–x cos x On integrating both sides with respect to x, we get ye– x = cos C ex x dx − + ∫ (1) Let I = excos x dx − ∫ = cos ( sin ) ( ) 1 x x xe x e dx − − ⎛ ⎞ − − − ⎜ ⎝−⎟ ⎠ ∫ © NCERT not to be republished MATHEMATICS 410 = cos sin x x x e x e dx − − − −∫ = cos sin (– ) cos ( ) x x x x e x e x e dx − − − ⎡ ⎤ − − − − ⎣ ⎦ ∫ = cos sin cos x x x x e x e x e dx − − − − + −∫ or I = – e–x cos x + sin x e–x – I or 2I = (sin x – cos x) e–x or I = (sin cos ) 2 x x x e− − Substituting the value of I in equation (1), we get ye– x = sin cos C 2 x x x e− − ⎛ ⎞ + ⎜ ⎟ ⎝ ⎠ or y = sin cos C 2 x x x e − ⎛ ⎞ + ⎜ ⎟ ⎝ ⎠ which is the general solution of the given differential equation
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4853-4856
F = 1 dx x e e Multiplying both sides of equation by I F, we get x x dy e e y dx − −− = e–x cos x or ( dy yex) dx − = e–x cos x On integrating both sides with respect to x, we get ye– x = cos C ex x dx − + ∫ (1) Let I = excos x dx − ∫ = cos ( sin ) ( ) 1 x x xe x e dx − − ⎛ ⎞ − − − ⎜ ⎝−⎟ ⎠ ∫ © NCERT not to be republished MATHEMATICS 410 = cos sin x x x e x e dx − − − −∫ = cos sin (– ) cos ( ) x x x x e x e x e dx − − − ⎡ ⎤ − − − − ⎣ ⎦ ∫ = cos sin cos x x x x e x e x e dx − − − − + −∫ or I = – e–x cos x + sin x e–x – I or 2I = (sin x – cos x) e–x or I = (sin cos ) 2 x x x e− − Substituting the value of I in equation (1), we get ye– x = sin cos C 2 x x x e− − ⎛ ⎞ + ⎜ ⎟ ⎝ ⎠ or y = sin cos C 2 x x x e − ⎛ ⎞ + ⎜ ⎟ ⎝ ⎠ which is the general solution of the given differential equation Example 20 Find the general solution of the differential equation 2 2 ( 0) xdy y x x dx + = ≠
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4854-4857
F, we get x x dy e e y dx − −− = e–x cos x or ( dy yex) dx − = e–x cos x On integrating both sides with respect to x, we get ye– x = cos C ex x dx − + ∫ (1) Let I = excos x dx − ∫ = cos ( sin ) ( ) 1 x x xe x e dx − − ⎛ ⎞ − − − ⎜ ⎝−⎟ ⎠ ∫ © NCERT not to be republished MATHEMATICS 410 = cos sin x x x e x e dx − − − −∫ = cos sin (– ) cos ( ) x x x x e x e x e dx − − − ⎡ ⎤ − − − − ⎣ ⎦ ∫ = cos sin cos x x x x e x e x e dx − − − − + −∫ or I = – e–x cos x + sin x e–x – I or 2I = (sin x – cos x) e–x or I = (sin cos ) 2 x x x e− − Substituting the value of I in equation (1), we get ye– x = sin cos C 2 x x x e− − ⎛ ⎞ + ⎜ ⎟ ⎝ ⎠ or y = sin cos C 2 x x x e − ⎛ ⎞ + ⎜ ⎟ ⎝ ⎠ which is the general solution of the given differential equation Example 20 Find the general solution of the differential equation 2 2 ( 0) xdy y x x dx + = ≠ Solution The given differential equation is 2 xdy dx +y = x2
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4855-4858
(1) Let I = excos x dx − ∫ = cos ( sin ) ( ) 1 x x xe x e dx − − ⎛ ⎞ − − − ⎜ ⎝−⎟ ⎠ ∫ © NCERT not to be republished MATHEMATICS 410 = cos sin x x x e x e dx − − − −∫ = cos sin (– ) cos ( ) x x x x e x e x e dx − − − ⎡ ⎤ − − − − ⎣ ⎦ ∫ = cos sin cos x x x x e x e x e dx − − − − + −∫ or I = – e–x cos x + sin x e–x – I or 2I = (sin x – cos x) e–x or I = (sin cos ) 2 x x x e− − Substituting the value of I in equation (1), we get ye– x = sin cos C 2 x x x e− − ⎛ ⎞ + ⎜ ⎟ ⎝ ⎠ or y = sin cos C 2 x x x e − ⎛ ⎞ + ⎜ ⎟ ⎝ ⎠ which is the general solution of the given differential equation Example 20 Find the general solution of the differential equation 2 2 ( 0) xdy y x x dx + = ≠ Solution The given differential equation is 2 xdy dx +y = x2 (1) Dividing both sides of equation (1) by x, we get 2 dy y dx +x = x which is a linear differential equation of the type P Q dy dx +y = , where 2 P =x and Q = x
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4856-4859
Example 20 Find the general solution of the differential equation 2 2 ( 0) xdy y x x dx + = ≠ Solution The given differential equation is 2 xdy dx +y = x2 (1) Dividing both sides of equation (1) by x, we get 2 dy y dx +x = x which is a linear differential equation of the type P Q dy dx +y = , where 2 P =x and Q = x So I
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4857-4860
Solution The given differential equation is 2 xdy dx +y = x2 (1) Dividing both sides of equation (1) by x, we get 2 dy y dx +x = x which is a linear differential equation of the type P Q dy dx +y = , where 2 P =x and Q = x So I F = e∫x2 dx = e2 log x = log2 2 x e =x log ( ) [ ( )] f x as e f x = Therefore, solution of the given equation is given by y
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4858-4861
(1) Dividing both sides of equation (1) by x, we get 2 dy y dx +x = x which is a linear differential equation of the type P Q dy dx +y = , where 2 P =x and Q = x So I F = e∫x2 dx = e2 log x = log2 2 x e =x log ( ) [ ( )] f x as e f x = Therefore, solution of the given equation is given by y x2 = ( ) (2 ) C x x dx + ∫ = 3 x dx +C ∫ or y = 2 2 C x4 x− + which is the general solution of the given differential equation
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4859-4862
So I F = e∫x2 dx = e2 log x = log2 2 x e =x log ( ) [ ( )] f x as e f x = Therefore, solution of the given equation is given by y x2 = ( ) (2 ) C x x dx + ∫ = 3 x dx +C ∫ or y = 2 2 C x4 x− + which is the general solution of the given differential equation © NCERT not to be republished DIFFERENTIAL EQUATIONS 411 Example 21 Find the general solution of the differential equation y dx – (x + 2y2) dy = 0
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F = e∫x2 dx = e2 log x = log2 2 x e =x log ( ) [ ( )] f x as e f x = Therefore, solution of the given equation is given by y x2 = ( ) (2 ) C x x dx + ∫ = 3 x dx +C ∫ or y = 2 2 C x4 x− + which is the general solution of the given differential equation © NCERT not to be republished DIFFERENTIAL EQUATIONS 411 Example 21 Find the general solution of the differential equation y dx – (x + 2y2) dy = 0 Solution The given differential equation can be written as dx x dy −y = 2y This is a linear differential equation of the type 1 1 P Q dx x dy + = , where 1 1 P = −y and Q1 = 2y
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4861-4864
x2 = ( ) (2 ) C x x dx + ∫ = 3 x dx +C ∫ or y = 2 2 C x4 x− + which is the general solution of the given differential equation © NCERT not to be republished DIFFERENTIAL EQUATIONS 411 Example 21 Find the general solution of the differential equation y dx – (x + 2y2) dy = 0 Solution The given differential equation can be written as dx x dy −y = 2y This is a linear differential equation of the type 1 1 P Q dx x dy + = , where 1 1 P = −y and Q1 = 2y Therefore 1 1 log log( ) 1 I
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4862-4865
© NCERT not to be republished DIFFERENTIAL EQUATIONS 411 Example 21 Find the general solution of the differential equation y dx – (x + 2y2) dy = 0 Solution The given differential equation can be written as dx x dy −y = 2y This is a linear differential equation of the type 1 1 P Q dx x dy + = , where 1 1 P = −y and Q1 = 2y Therefore 1 1 log log( ) 1 I F dy y y y e e e y − − − =∫ = = = Hence, the solution of the given differential equation is 1 x y = 1 (2 ) C y ⎛ydy ⎞ + ⎜ ⎟ ⎝ ⎠ ∫ or x y = (2 ) dy +C ∫ or x y = 2y + C or x = 2y2 + Cy which is a general solution of the given differential equation
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4863-4866
Solution The given differential equation can be written as dx x dy −y = 2y This is a linear differential equation of the type 1 1 P Q dx x dy + = , where 1 1 P = −y and Q1 = 2y Therefore 1 1 log log( ) 1 I F dy y y y e e e y − − − =∫ = = = Hence, the solution of the given differential equation is 1 x y = 1 (2 ) C y ⎛ydy ⎞ + ⎜ ⎟ ⎝ ⎠ ∫ or x y = (2 ) dy +C ∫ or x y = 2y + C or x = 2y2 + Cy which is a general solution of the given differential equation Example 22 Find the particular solution of the differential equation cot dy+ y x dx = 2x + x2 cot x (x ≠ 0) given that y = 0 when 2 x =π
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4864-4867
Therefore 1 1 log log( ) 1 I F dy y y y e e e y − − − =∫ = = = Hence, the solution of the given differential equation is 1 x y = 1 (2 ) C y ⎛ydy ⎞ + ⎜ ⎟ ⎝ ⎠ ∫ or x y = (2 ) dy +C ∫ or x y = 2y + C or x = 2y2 + Cy which is a general solution of the given differential equation Example 22 Find the particular solution of the differential equation cot dy+ y x dx = 2x + x2 cot x (x ≠ 0) given that y = 0 when 2 x =π Solution The given equation is a linear differential equation of the type P Q dy dx +y = , where P = cot x and Q = 2x + x2 cot x
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4865-4868
F dy y y y e e e y − − − =∫ = = = Hence, the solution of the given differential equation is 1 x y = 1 (2 ) C y ⎛ydy ⎞ + ⎜ ⎟ ⎝ ⎠ ∫ or x y = (2 ) dy +C ∫ or x y = 2y + C or x = 2y2 + Cy which is a general solution of the given differential equation Example 22 Find the particular solution of the differential equation cot dy+ y x dx = 2x + x2 cot x (x ≠ 0) given that y = 0 when 2 x =π Solution The given equation is a linear differential equation of the type P Q dy dx +y = , where P = cot x and Q = 2x + x2 cot x Therefore I
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4866-4869
Example 22 Find the particular solution of the differential equation cot dy+ y x dx = 2x + x2 cot x (x ≠ 0) given that y = 0 when 2 x =π Solution The given equation is a linear differential equation of the type P Q dy dx +y = , where P = cot x and Q = 2x + x2 cot x Therefore I F = cot log sin sin x dx x e e x Hence, the solution of the differential equation is given by y
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4867-4870
Solution The given equation is a linear differential equation of the type P Q dy dx +y = , where P = cot x and Q = 2x + x2 cot x Therefore I F = cot log sin sin x dx x e e x Hence, the solution of the differential equation is given by y sin x = ∫(2x + x2 cot x) sin x dx + C © NCERT not to be republished MATHEMATICS 412 or y sin x = ∫ 2x sin x dx + ∫x2 cos x dx + C or y sin x = 2 2 2 2 2 sin cos cos C 2 2 x x x x dx x x dx ⎛ ⎞ ⎛ ⎞ − + + ⎜ ⎟ ⎜ ⎟ ⎝ ⎠ ⎝ ⎠ ∫ ∫ or y sin x = 2 2 2 sin cos cos C x x x x dx x x dx − + + ∫ ∫ or y sin x = x2 sin x + C
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4868-4871
Therefore I F = cot log sin sin x dx x e e x Hence, the solution of the differential equation is given by y sin x = ∫(2x + x2 cot x) sin x dx + C © NCERT not to be republished MATHEMATICS 412 or y sin x = ∫ 2x sin x dx + ∫x2 cos x dx + C or y sin x = 2 2 2 2 2 sin cos cos C 2 2 x x x x dx x x dx ⎛ ⎞ ⎛ ⎞ − + + ⎜ ⎟ ⎜ ⎟ ⎝ ⎠ ⎝ ⎠ ∫ ∫ or y sin x = 2 2 2 sin cos cos C x x x x dx x x dx − + + ∫ ∫ or y sin x = x2 sin x + C (1) Substituting y = 0 and 2 x =π in equation (1), we get 0 = 2 sin C 2 2 π π ⎛ ⎞ ⎛ ⎞ + ⎜ ⎟ ⎜ ⎟ ⎝ ⎠ ⎝ ⎠ or C = 2 4 −π Substituting the value of C in equation (1), we get y sin x = 2 2 sin 4 x x π − or y = 2 2 (sin 0) 4 sin x x πx − ≠ which is the particular solution of the given differential equation
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4869-4872
F = cot log sin sin x dx x e e x Hence, the solution of the differential equation is given by y sin x = ∫(2x + x2 cot x) sin x dx + C © NCERT not to be republished MATHEMATICS 412 or y sin x = ∫ 2x sin x dx + ∫x2 cos x dx + C or y sin x = 2 2 2 2 2 sin cos cos C 2 2 x x x x dx x x dx ⎛ ⎞ ⎛ ⎞ − + + ⎜ ⎟ ⎜ ⎟ ⎝ ⎠ ⎝ ⎠ ∫ ∫ or y sin x = 2 2 2 sin cos cos C x x x x dx x x dx − + + ∫ ∫ or y sin x = x2 sin x + C (1) Substituting y = 0 and 2 x =π in equation (1), we get 0 = 2 sin C 2 2 π π ⎛ ⎞ ⎛ ⎞ + ⎜ ⎟ ⎜ ⎟ ⎝ ⎠ ⎝ ⎠ or C = 2 4 −π Substituting the value of C in equation (1), we get y sin x = 2 2 sin 4 x x π − or y = 2 2 (sin 0) 4 sin x x πx − ≠ which is the particular solution of the given differential equation Example 23 Find the equation of a curve passing through the point (0, 1)
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4870-4873
sin x = ∫(2x + x2 cot x) sin x dx + C © NCERT not to be republished MATHEMATICS 412 or y sin x = ∫ 2x sin x dx + ∫x2 cos x dx + C or y sin x = 2 2 2 2 2 sin cos cos C 2 2 x x x x dx x x dx ⎛ ⎞ ⎛ ⎞ − + + ⎜ ⎟ ⎜ ⎟ ⎝ ⎠ ⎝ ⎠ ∫ ∫ or y sin x = 2 2 2 sin cos cos C x x x x dx x x dx − + + ∫ ∫ or y sin x = x2 sin x + C (1) Substituting y = 0 and 2 x =π in equation (1), we get 0 = 2 sin C 2 2 π π ⎛ ⎞ ⎛ ⎞ + ⎜ ⎟ ⎜ ⎟ ⎝ ⎠ ⎝ ⎠ or C = 2 4 −π Substituting the value of C in equation (1), we get y sin x = 2 2 sin 4 x x π − or y = 2 2 (sin 0) 4 sin x x πx − ≠ which is the particular solution of the given differential equation Example 23 Find the equation of a curve passing through the point (0, 1) If the slope of the tangent to the curve at any point (x, y) is equal to the sum of the x coordinate (abscissa) and the product of the x coordinate and y coordinate (ordinate) of that point
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4871-4874
(1) Substituting y = 0 and 2 x =π in equation (1), we get 0 = 2 sin C 2 2 π π ⎛ ⎞ ⎛ ⎞ + ⎜ ⎟ ⎜ ⎟ ⎝ ⎠ ⎝ ⎠ or C = 2 4 −π Substituting the value of C in equation (1), we get y sin x = 2 2 sin 4 x x π − or y = 2 2 (sin 0) 4 sin x x πx − ≠ which is the particular solution of the given differential equation Example 23 Find the equation of a curve passing through the point (0, 1) If the slope of the tangent to the curve at any point (x, y) is equal to the sum of the x coordinate (abscissa) and the product of the x coordinate and y coordinate (ordinate) of that point Solution We know that the slope of the tangent to the curve is dy dx
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4872-4875
Example 23 Find the equation of a curve passing through the point (0, 1) If the slope of the tangent to the curve at any point (x, y) is equal to the sum of the x coordinate (abscissa) and the product of the x coordinate and y coordinate (ordinate) of that point Solution We know that the slope of the tangent to the curve is dy dx Therefore, dy dx = x + xy or dy dx −xy = x
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4873-4876
If the slope of the tangent to the curve at any point (x, y) is equal to the sum of the x coordinate (abscissa) and the product of the x coordinate and y coordinate (ordinate) of that point Solution We know that the slope of the tangent to the curve is dy dx Therefore, dy dx = x + xy or dy dx −xy = x (1) This is a linear differential equation of the type P Q dy dx +y = , where P = – x and Q = x
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4874-4877
Solution We know that the slope of the tangent to the curve is dy dx Therefore, dy dx = x + xy or dy dx −xy = x (1) This is a linear differential equation of the type P Q dy dx +y = , where P = – x and Q = x Therefore, I
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4875-4878
Therefore, dy dx = x + xy or dy dx −xy = x (1) This is a linear differential equation of the type P Q dy dx +y = , where P = – x and Q = x Therefore, I F = 2 2 x x dx e e − −∫ = © NCERT not to be republished DIFFERENTIAL EQUATIONS 413 Hence, the solution of equation is given by 2 2 x y e ⋅− = ( ) 2 2 ( ) C x x dx e − + ∫
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4876-4879
(1) This is a linear differential equation of the type P Q dy dx +y = , where P = – x and Q = x Therefore, I F = 2 2 x x dx e e − −∫ = © NCERT not to be republished DIFFERENTIAL EQUATIONS 413 Hence, the solution of equation is given by 2 2 x y e ⋅− = ( ) 2 2 ( ) C x x dx e − + ∫ (2) Let I = 2 2 ( ) x x dx e − ∫ Let 2 x2 t − = , then – x dx = dt or x dx = – dt
1
4877-4880
Therefore, I F = 2 2 x x dx e e − −∫ = © NCERT not to be republished DIFFERENTIAL EQUATIONS 413 Hence, the solution of equation is given by 2 2 x y e ⋅− = ( ) 2 2 ( ) C x x dx e − + ∫ (2) Let I = 2 2 ( ) x x dx e − ∫ Let 2 x2 t − = , then – x dx = dt or x dx = – dt Therefore, I = 2 2 – x t t e dt e e − − = − = ∫ Substituting the value of I in equation (2), we get 2 2 x y e − = 2 2 + C x e or y = 2 2 1 C x e − +
1
4878-4881
F = 2 2 x x dx e e − −∫ = © NCERT not to be republished DIFFERENTIAL EQUATIONS 413 Hence, the solution of equation is given by 2 2 x y e ⋅− = ( ) 2 2 ( ) C x x dx e − + ∫ (2) Let I = 2 2 ( ) x x dx e − ∫ Let 2 x2 t − = , then – x dx = dt or x dx = – dt Therefore, I = 2 2 – x t t e dt e e − − = − = ∫ Substituting the value of I in equation (2), we get 2 2 x y e − = 2 2 + C x e or y = 2 2 1 C x e − + (3) Now (3) represents the equation of family of curves
1
4879-4882
(2) Let I = 2 2 ( ) x x dx e − ∫ Let 2 x2 t − = , then – x dx = dt or x dx = – dt Therefore, I = 2 2 – x t t e dt e e − − = − = ∫ Substituting the value of I in equation (2), we get 2 2 x y e − = 2 2 + C x e or y = 2 2 1 C x e − + (3) Now (3) represents the equation of family of curves But we are interested in finding a particular member of the family passing through (0, 1)
1
4880-4883
Therefore, I = 2 2 – x t t e dt e e − − = − = ∫ Substituting the value of I in equation (2), we get 2 2 x y e − = 2 2 + C x e or y = 2 2 1 C x e − + (3) Now (3) represents the equation of family of curves But we are interested in finding a particular member of the family passing through (0, 1) Substituting x = 0 and y = 1 in equation (3) we get 1 = – 1 + C
1
4881-4884
(3) Now (3) represents the equation of family of curves But we are interested in finding a particular member of the family passing through (0, 1) Substituting x = 0 and y = 1 in equation (3) we get 1 = – 1 + C e0 or C = 2 Substituting the value of C in equation (3), we get y = 2 2 1 2 x e − + which is the equation of the required curve
1
4882-4885
But we are interested in finding a particular member of the family passing through (0, 1) Substituting x = 0 and y = 1 in equation (3) we get 1 = – 1 + C e0 or C = 2 Substituting the value of C in equation (3), we get y = 2 2 1 2 x e − + which is the equation of the required curve EXERCISE 9
1
4883-4886
Substituting x = 0 and y = 1 in equation (3) we get 1 = – 1 + C e0 or C = 2 Substituting the value of C in equation (3), we get y = 2 2 1 2 x e − + which is the equation of the required curve EXERCISE 9 6 For each of the differential equations given in Exercises 1 to 12, find the general solution: 1
1
4884-4887
e0 or C = 2 Substituting the value of C in equation (3), we get y = 2 2 1 2 x e − + which is the equation of the required curve EXERCISE 9 6 For each of the differential equations given in Exercises 1 to 12, find the general solution: 1 2 sin dy y x dx + = 2
1
4885-4888
EXERCISE 9 6 For each of the differential equations given in Exercises 1 to 12, find the general solution: 1 2 sin dy y x dx + = 2 2 3 x dy y e dx − + = 3
1
4886-4889
6 For each of the differential equations given in Exercises 1 to 12, find the general solution: 1 2 sin dy y x dx + = 2 2 3 x dy y e dx − + = 3 2 dy y x dx +x = 4
1
4887-4890
2 sin dy y x dx + = 2 2 3 x dy y e dx − + = 3 2 dy y x dx +x = 4 (sec ) tan 0 2 dy x y x x dx π ⎛ ⎞ + = ≤ < ⎜ ⎟ ⎝ ⎠ 5
1
4888-4891
2 3 x dy y e dx − + = 3 2 dy y x dx +x = 4 (sec ) tan 0 2 dy x y x x dx π ⎛ ⎞ + = ≤ < ⎜ ⎟ ⎝ ⎠ 5 cos2 tan xdy y x dx + = 0 2 x π ⎛ ⎞ ≤ < ⎜ ⎟ ⎝ ⎠ 6
1
4889-4892
2 dy y x dx +x = 4 (sec ) tan 0 2 dy x y x x dx π ⎛ ⎞ + = ≤ < ⎜ ⎟ ⎝ ⎠ 5 cos2 tan xdy y x dx + = 0 2 x π ⎛ ⎞ ≤ < ⎜ ⎟ ⎝ ⎠ 6 2 2 log xdy y x x dx + = 7
1
4890-4893
(sec ) tan 0 2 dy x y x x dx π ⎛ ⎞ + = ≤ < ⎜ ⎟ ⎝ ⎠ 5 cos2 tan xdy y x dx + = 0 2 x π ⎛ ⎞ ≤ < ⎜ ⎟ ⎝ ⎠ 6 2 2 log xdy y x x dx + = 7 2 log log dy x x y x dx x + = 8
1
4891-4894
cos2 tan xdy y x dx + = 0 2 x π ⎛ ⎞ ≤ < ⎜ ⎟ ⎝ ⎠ 6 2 2 log xdy y x x dx + = 7 2 log log dy x x y x dx x + = 8 (1 + x2) dy + 2xy dx = cot x dx (x ≠ 0) © NCERT not to be republished MATHEMATICS 414 9
1
4892-4895
2 2 log xdy y x x dx + = 7 2 log log dy x x y x dx x + = 8 (1 + x2) dy + 2xy dx = cot x dx (x ≠ 0) © NCERT not to be republished MATHEMATICS 414 9 cot 0 ( 0) xdy y x xy x x dx + − + = ≠ 10
1
4893-4896
2 log log dy x x y x dx x + = 8 (1 + x2) dy + 2xy dx = cot x dx (x ≠ 0) © NCERT not to be republished MATHEMATICS 414 9 cot 0 ( 0) xdy y x xy x x dx + − + = ≠ 10 ( ) 1 dy x +y dx = 11
1
4894-4897
(1 + x2) dy + 2xy dx = cot x dx (x ≠ 0) © NCERT not to be republished MATHEMATICS 414 9 cot 0 ( 0) xdy y x xy x x dx + − + = ≠ 10 ( ) 1 dy x +y dx = 11 y dx + (x – y2) dy = 0 12
1
4895-4898
cot 0 ( 0) xdy y x xy x x dx + − + = ≠ 10 ( ) 1 dy x +y dx = 11 y dx + (x – y2) dy = 0 12 2 ( 3 ) ( 0) dy x y y y dx + = >
1
4896-4899
( ) 1 dy x +y dx = 11 y dx + (x – y2) dy = 0 12 2 ( 3 ) ( 0) dy x y y y dx + = > For each of the differential equations given in Exercises 13 to 15, find a particular solution satisfying the given condition: 13
1
4897-4900
y dx + (x – y2) dy = 0 12 2 ( 3 ) ( 0) dy x y y y dx + = > For each of the differential equations given in Exercises 13 to 15, find a particular solution satisfying the given condition: 13 2 tan sin ; 0 when 3 dy y x x y x dx π + = = = 14
1
4898-4901
2 ( 3 ) ( 0) dy x y y y dx + = > For each of the differential equations given in Exercises 13 to 15, find a particular solution satisfying the given condition: 13 2 tan sin ; 0 when 3 dy y x x y x dx π + = = = 14 2 12 (1 ) 2 ; 0 when 1 1 dy x xy y x dx x + + = = = + 15
1
4899-4902
For each of the differential equations given in Exercises 13 to 15, find a particular solution satisfying the given condition: 13 2 tan sin ; 0 when 3 dy y x x y x dx π + = = = 14 2 12 (1 ) 2 ; 0 when 1 1 dy x xy y x dx x + + = = = + 15 3 cot sin2 ; 2 when 2 dy y x x y x dx π − = = = 16
1
4900-4903
2 tan sin ; 0 when 3 dy y x x y x dx π + = = = 14 2 12 (1 ) 2 ; 0 when 1 1 dy x xy y x dx x + + = = = + 15 3 cot sin2 ; 2 when 2 dy y x x y x dx π − = = = 16 Find the equation of a curve passing through the origin given that the slope of the tangent to the curve at any point (x, y) is equal to the sum of the coordinates of the point
1
4901-4904
2 12 (1 ) 2 ; 0 when 1 1 dy x xy y x dx x + + = = = + 15 3 cot sin2 ; 2 when 2 dy y x x y x dx π − = = = 16 Find the equation of a curve passing through the origin given that the slope of the tangent to the curve at any point (x, y) is equal to the sum of the coordinates of the point 17
1
4902-4905
3 cot sin2 ; 2 when 2 dy y x x y x dx π − = = = 16 Find the equation of a curve passing through the origin given that the slope of the tangent to the curve at any point (x, y) is equal to the sum of the coordinates of the point 17 Find the equation of a curve passing through the point (0, 2) given that the sum of the coordinates of any point on the curve exceeds the magnitude of the slope of the tangent to the curve at that point by 5
1
4903-4906
Find the equation of a curve passing through the origin given that the slope of the tangent to the curve at any point (x, y) is equal to the sum of the coordinates of the point 17 Find the equation of a curve passing through the point (0, 2) given that the sum of the coordinates of any point on the curve exceeds the magnitude of the slope of the tangent to the curve at that point by 5 18
1
4904-4907
17 Find the equation of a curve passing through the point (0, 2) given that the sum of the coordinates of any point on the curve exceeds the magnitude of the slope of the tangent to the curve at that point by 5 18 The Integrating Factor of the differential equation 22 xdy y x dx − = is (A) e–x (B) e–y (C) 1 x (D) x 19
1
4905-4908
Find the equation of a curve passing through the point (0, 2) given that the sum of the coordinates of any point on the curve exceeds the magnitude of the slope of the tangent to the curve at that point by 5 18 The Integrating Factor of the differential equation 22 xdy y x dx − = is (A) e–x (B) e–y (C) 1 x (D) x 19 The Integrating Factor of the differential equation 2 (1 y) dx yx dy − + = ( 1 1) ay y is (A) 12 y 1 (B) 2 1 y −1 (C) 112 −y (D) 2 1 1 y − Miscellaneous Examples Example 24 Verify that the function y = c1 eax cos bx + c2 eax sin bx, where c1, c2 are arbitrary constants is a solution of the differential equation ( ) 2 2 2 2 2 0 d y ady a b y dx dx − + + = © NCERT not to be republished DIFFERENTIAL EQUATIONS 415 Solution The given function is y = eax [c1 cosbx + c2 sinbx]
1
4906-4909
18 The Integrating Factor of the differential equation 22 xdy y x dx − = is (A) e–x (B) e–y (C) 1 x (D) x 19 The Integrating Factor of the differential equation 2 (1 y) dx yx dy − + = ( 1 1) ay y is (A) 12 y 1 (B) 2 1 y −1 (C) 112 −y (D) 2 1 1 y − Miscellaneous Examples Example 24 Verify that the function y = c1 eax cos bx + c2 eax sin bx, where c1, c2 are arbitrary constants is a solution of the differential equation ( ) 2 2 2 2 2 0 d y ady a b y dx dx − + + = © NCERT not to be republished DIFFERENTIAL EQUATIONS 415 Solution The given function is y = eax [c1 cosbx + c2 sinbx] (1) Differentiating both sides of equation (1) with respect to x, we get dy dx = 1 2 1 2 – sin cos cos sin ax ax e bc bx bc bx c bx c bx e a or dy dx = 2 1 2 1 [( )cos ( )sin ] eax bc ac bx ac bc bx + + −
1
4907-4910
The Integrating Factor of the differential equation 22 xdy y x dx − = is (A) e–x (B) e–y (C) 1 x (D) x 19 The Integrating Factor of the differential equation 2 (1 y) dx yx dy − + = ( 1 1) ay y is (A) 12 y 1 (B) 2 1 y −1 (C) 112 −y (D) 2 1 1 y − Miscellaneous Examples Example 24 Verify that the function y = c1 eax cos bx + c2 eax sin bx, where c1, c2 are arbitrary constants is a solution of the differential equation ( ) 2 2 2 2 2 0 d y ady a b y dx dx − + + = © NCERT not to be republished DIFFERENTIAL EQUATIONS 415 Solution The given function is y = eax [c1 cosbx + c2 sinbx] (1) Differentiating both sides of equation (1) with respect to x, we get dy dx = 1 2 1 2 – sin cos cos sin ax ax e bc bx bc bx c bx c bx e a or dy dx = 2 1 2 1 [( )cos ( )sin ] eax bc ac bx ac bc bx + + − (2) Differentiating both sides of equation (2) with respect to x, we get 2 d y2 dx = 2 1 2 1 [( ) ( sin ) ( ) ( cos )] eax bc ac b bx ac bc b bx + 2 1 2 1 [( ) cos ( ) sin ] ax
1
4908-4911
The Integrating Factor of the differential equation 2 (1 y) dx yx dy − + = ( 1 1) ay y is (A) 12 y 1 (B) 2 1 y −1 (C) 112 −y (D) 2 1 1 y − Miscellaneous Examples Example 24 Verify that the function y = c1 eax cos bx + c2 eax sin bx, where c1, c2 are arbitrary constants is a solution of the differential equation ( ) 2 2 2 2 2 0 d y ady a b y dx dx − + + = © NCERT not to be republished DIFFERENTIAL EQUATIONS 415 Solution The given function is y = eax [c1 cosbx + c2 sinbx] (1) Differentiating both sides of equation (1) with respect to x, we get dy dx = 1 2 1 2 – sin cos cos sin ax ax e bc bx bc bx c bx c bx e a or dy dx = 2 1 2 1 [( )cos ( )sin ] eax bc ac bx ac bc bx + + − (2) Differentiating both sides of equation (2) with respect to x, we get 2 d y2 dx = 2 1 2 1 [( ) ( sin ) ( ) ( cos )] eax bc ac b bx ac bc b bx + 2 1 2 1 [( ) cos ( ) sin ] ax bc ac bx ac bc bx e a + + − = 2 2 2 2 2 1 2 1 2 1 [( 2 ) sin ( 2 ) cos ] eax a c abc b c bx a c abc b c bx − − + + − Substituting the values of 2 2 , d y dy dx dx and y in the given differential equation, we get L
1
4909-4912
(1) Differentiating both sides of equation (1) with respect to x, we get dy dx = 1 2 1 2 – sin cos cos sin ax ax e bc bx bc bx c bx c bx e a or dy dx = 2 1 2 1 [( )cos ( )sin ] eax bc ac bx ac bc bx + + − (2) Differentiating both sides of equation (2) with respect to x, we get 2 d y2 dx = 2 1 2 1 [( ) ( sin ) ( ) ( cos )] eax bc ac b bx ac bc b bx + 2 1 2 1 [( ) cos ( ) sin ] ax bc ac bx ac bc bx e a + + − = 2 2 2 2 2 1 2 1 2 1 [( 2 ) sin ( 2 ) cos ] eax a c abc b c bx a c abc b c bx − − + + − Substituting the values of 2 2 , d y dy dx dx and y in the given differential equation, we get L H
1
4910-4913
(2) Differentiating both sides of equation (2) with respect to x, we get 2 d y2 dx = 2 1 2 1 [( ) ( sin ) ( ) ( cos )] eax bc ac b bx ac bc b bx + 2 1 2 1 [( ) cos ( ) sin ] ax bc ac bx ac bc bx e a + + − = 2 2 2 2 2 1 2 1 2 1 [( 2 ) sin ( 2 ) cos ] eax a c abc b c bx a c abc b c bx − − + + − Substituting the values of 2 2 , d y dy dx dx and y in the given differential equation, we get L H S
1
4911-4914
bc ac bx ac bc bx e a + + − = 2 2 2 2 2 1 2 1 2 1 [( 2 ) sin ( 2 ) cos ] eax a c abc b c bx a c abc b c bx − − + + − Substituting the values of 2 2 , d y dy dx dx and y in the given differential equation, we get L H S = 2 2 2 2 2 1 2 1 2 1 [ 2 )sin ( 2 )cos ] eax a c abc b c bx a c abc b c bx − − + + − 2 1 2 1 2 [( )cos ( )sin ] aeax bc ac bx ac bc bx 2 2 1 2 ( ) [ cos sin ] ax a b e c bx c bx = ( ) 2 2 2 2 2 2 1 2 2 1 2 2 2 2 2 2 2 1 2 1 2 1 1 1 2 2 2 sin ( 2 2 2 )cos ax a c abc b c a c abc a c b c bx e a c abc b c abc a c a c b c bx ⎡ ⎤ − − − + + + ⎢ ⎥ ⎢ ⎥ + + − − − + + ⎣ ⎦ = [0 sin 0cos ] eax bx bx × + = eax × 0 = 0 = R
1
4912-4915
H S = 2 2 2 2 2 1 2 1 2 1 [ 2 )sin ( 2 )cos ] eax a c abc b c bx a c abc b c bx − − + + − 2 1 2 1 2 [( )cos ( )sin ] aeax bc ac bx ac bc bx 2 2 1 2 ( ) [ cos sin ] ax a b e c bx c bx = ( ) 2 2 2 2 2 2 1 2 2 1 2 2 2 2 2 2 2 1 2 1 2 1 1 1 2 2 2 sin ( 2 2 2 )cos ax a c abc b c a c abc a c b c bx e a c abc b c abc a c a c b c bx ⎡ ⎤ − − − + + + ⎢ ⎥ ⎢ ⎥ + + − − − + + ⎣ ⎦ = [0 sin 0cos ] eax bx bx × + = eax × 0 = 0 = R H
1
4913-4916
S = 2 2 2 2 2 1 2 1 2 1 [ 2 )sin ( 2 )cos ] eax a c abc b c bx a c abc b c bx − − + + − 2 1 2 1 2 [( )cos ( )sin ] aeax bc ac bx ac bc bx 2 2 1 2 ( ) [ cos sin ] ax a b e c bx c bx = ( ) 2 2 2 2 2 2 1 2 2 1 2 2 2 2 2 2 2 1 2 1 2 1 1 1 2 2 2 sin ( 2 2 2 )cos ax a c abc b c a c abc a c b c bx e a c abc b c abc a c a c b c bx ⎡ ⎤ − − − + + + ⎢ ⎥ ⎢ ⎥ + + − − − + + ⎣ ⎦ = [0 sin 0cos ] eax bx bx × + = eax × 0 = 0 = R H S
1
4914-4917
= 2 2 2 2 2 1 2 1 2 1 [ 2 )sin ( 2 )cos ] eax a c abc b c bx a c abc b c bx − − + + − 2 1 2 1 2 [( )cos ( )sin ] aeax bc ac bx ac bc bx 2 2 1 2 ( ) [ cos sin ] ax a b e c bx c bx = ( ) 2 2 2 2 2 2 1 2 2 1 2 2 2 2 2 2 2 1 2 1 2 1 1 1 2 2 2 sin ( 2 2 2 )cos ax a c abc b c a c abc a c b c bx e a c abc b c abc a c a c b c bx ⎡ ⎤ − − − + + + ⎢ ⎥ ⎢ ⎥ + + − − − + + ⎣ ⎦ = [0 sin 0cos ] eax bx bx × + = eax × 0 = 0 = R H S Hence, the given function is a solution of the given differential equation
1
4915-4918
H S Hence, the given function is a solution of the given differential equation Example 25 Form the differential equation of the family of circles in the second quadrant and touching the coordinate axes
1
4916-4919
S Hence, the given function is a solution of the given differential equation Example 25 Form the differential equation of the family of circles in the second quadrant and touching the coordinate axes Solution Let C denote the family of circles in the second quadrant and touching the coordinate axes
1
4917-4920
Hence, the given function is a solution of the given differential equation Example 25 Form the differential equation of the family of circles in the second quadrant and touching the coordinate axes Solution Let C denote the family of circles in the second quadrant and touching the coordinate axes Let (–a, a) be the coordinate of the centre of any member of this family (see Fig 9