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1
2018-2021
The derivative of f at c is defined by 0 ( ) ( ) lim h f c h f c h → + − Rationalised 2023-24 CONTINUITY AND DIFFERENTIABILITY 119 f (x) xn sin x cos x tan x f ′(x) nxn – 1 cos x – sin x sec2 x provided this limit exists Derivative of f at c is denoted by f ′(c) or ( ( )) |c d dxf x The function defined by 0 ( ) ( ) ( ) lim h f x h f x f x h → + − ′ = wherever the limit exists is defined to be the derivative of f The derivative of f is denoted by f ′(x) or d( ( )) dxf x or if y = f (x) by dy dx or y′
1
2019-2022
Derivative of f at c is denoted by f ′(c) or ( ( )) |c d dxf x The function defined by 0 ( ) ( ) ( ) lim h f x h f x f x h → + − ′ = wherever the limit exists is defined to be the derivative of f The derivative of f is denoted by f ′(x) or d( ( )) dxf x or if y = f (x) by dy dx or y′ The process of finding derivative of a function is called differentiation
1
2020-2023
The function defined by 0 ( ) ( ) ( ) lim h f x h f x f x h → + − ′ = wherever the limit exists is defined to be the derivative of f The derivative of f is denoted by f ′(x) or d( ( )) dxf x or if y = f (x) by dy dx or y′ The process of finding derivative of a function is called differentiation We also use the phrase differentiate f(x) with respect to x to mean find f ′(x)
1
2021-2024
The derivative of f is denoted by f ′(x) or d( ( )) dxf x or if y = f (x) by dy dx or y′ The process of finding derivative of a function is called differentiation We also use the phrase differentiate f(x) with respect to x to mean find f ′(x) (1)The following rules were established as a part of algebra of derivatives: (u ± v)′ = u′ ± v′ (2) (uv)′ = u′v + uv′ (Leibnitz or product rule) (3) 2 u u v uv v v ′ ′ − ′   =     , wherever v ≠ 0 (Quotient rule)
1
2022-2025
The process of finding derivative of a function is called differentiation We also use the phrase differentiate f(x) with respect to x to mean find f ′(x) (1)The following rules were established as a part of algebra of derivatives: (u ± v)′ = u′ ± v′ (2) (uv)′ = u′v + uv′ (Leibnitz or product rule) (3) 2 u u v uv v v ′ ′ − ′   =     , wherever v ≠ 0 (Quotient rule) The following table gives a list of derivatives of certain standard functions: Table 5
1
2023-2026
We also use the phrase differentiate f(x) with respect to x to mean find f ′(x) (1)The following rules were established as a part of algebra of derivatives: (u ± v)′ = u′ ± v′ (2) (uv)′ = u′v + uv′ (Leibnitz or product rule) (3) 2 u u v uv v v ′ ′ − ′   =     , wherever v ≠ 0 (Quotient rule) The following table gives a list of derivatives of certain standard functions: Table 5 3 Whenever we defined derivative, we had put a caution provided the limit exists
1
2024-2027
(1)The following rules were established as a part of algebra of derivatives: (u ± v)′ = u′ ± v′ (2) (uv)′ = u′v + uv′ (Leibnitz or product rule) (3) 2 u u v uv v v ′ ′ − ′   =     , wherever v ≠ 0 (Quotient rule) The following table gives a list of derivatives of certain standard functions: Table 5 3 Whenever we defined derivative, we had put a caution provided the limit exists Now the natural question is; what if it doesn’t
1
2025-2028
The following table gives a list of derivatives of certain standard functions: Table 5 3 Whenever we defined derivative, we had put a caution provided the limit exists Now the natural question is; what if it doesn’t The question is quite pertinent and so is its answer
1
2026-2029
3 Whenever we defined derivative, we had put a caution provided the limit exists Now the natural question is; what if it doesn’t The question is quite pertinent and so is its answer If 0 ( ) ( ) lim h f c h f c h → + − does not exist, we say that f is not differentiable at c
1
2027-2030
Now the natural question is; what if it doesn’t The question is quite pertinent and so is its answer If 0 ( ) ( ) lim h f c h f c h → + − does not exist, we say that f is not differentiable at c In other words, we say that a function f is differentiable at a point c in its domain if both – 0 ( ) ( ) lim h f c h f c h → + − and 0 ( ) ( ) lim h f c h f c h + → + − are finite and equal
1
2028-2031
The question is quite pertinent and so is its answer If 0 ( ) ( ) lim h f c h f c h → + − does not exist, we say that f is not differentiable at c In other words, we say that a function f is differentiable at a point c in its domain if both – 0 ( ) ( ) lim h f c h f c h → + − and 0 ( ) ( ) lim h f c h f c h + → + − are finite and equal A function is said to be differentiable in an interval [a, b] if it is differentiable at every point of [a, b]
1
2029-2032
If 0 ( ) ( ) lim h f c h f c h → + − does not exist, we say that f is not differentiable at c In other words, we say that a function f is differentiable at a point c in its domain if both – 0 ( ) ( ) lim h f c h f c h → + − and 0 ( ) ( ) lim h f c h f c h + → + − are finite and equal A function is said to be differentiable in an interval [a, b] if it is differentiable at every point of [a, b] As in case of continuity, at the end points a and b, we take the right hand limit and left hand limit, which are nothing but left hand derivative and right hand derivative of the function at a and b respectively
1
2030-2033
In other words, we say that a function f is differentiable at a point c in its domain if both – 0 ( ) ( ) lim h f c h f c h → + − and 0 ( ) ( ) lim h f c h f c h + → + − are finite and equal A function is said to be differentiable in an interval [a, b] if it is differentiable at every point of [a, b] As in case of continuity, at the end points a and b, we take the right hand limit and left hand limit, which are nothing but left hand derivative and right hand derivative of the function at a and b respectively Similarly, a function is said to be differentiable in an interval (a, b) if it is differentiable at every point of (a, b)
1
2031-2034
A function is said to be differentiable in an interval [a, b] if it is differentiable at every point of [a, b] As in case of continuity, at the end points a and b, we take the right hand limit and left hand limit, which are nothing but left hand derivative and right hand derivative of the function at a and b respectively Similarly, a function is said to be differentiable in an interval (a, b) if it is differentiable at every point of (a, b) Rationalised 2023-24 MATHEMATICS 120 Theorem 3 If a function f is differentiable at a point c, then it is also continuous at that point
1
2032-2035
As in case of continuity, at the end points a and b, we take the right hand limit and left hand limit, which are nothing but left hand derivative and right hand derivative of the function at a and b respectively Similarly, a function is said to be differentiable in an interval (a, b) if it is differentiable at every point of (a, b) Rationalised 2023-24 MATHEMATICS 120 Theorem 3 If a function f is differentiable at a point c, then it is also continuous at that point Proof Since f is differentiable at c, we have ( ) ( ) lim ( ) x c f x f c f c x c → − = ′ − But for x ≠ c, we have f (x) – f (c) = ( ) ( )
1
2033-2036
Similarly, a function is said to be differentiable in an interval (a, b) if it is differentiable at every point of (a, b) Rationalised 2023-24 MATHEMATICS 120 Theorem 3 If a function f is differentiable at a point c, then it is also continuous at that point Proof Since f is differentiable at c, we have ( ) ( ) lim ( ) x c f x f c f c x c → − = ′ − But for x ≠ c, we have f (x) – f (c) = ( ) ( ) ( ) f x f c x c x c − − − Therefore lim[ ( ) ( )] x c f x f c → − = ( ) ( ) lim
1
2034-2037
Rationalised 2023-24 MATHEMATICS 120 Theorem 3 If a function f is differentiable at a point c, then it is also continuous at that point Proof Since f is differentiable at c, we have ( ) ( ) lim ( ) x c f x f c f c x c → − = ′ − But for x ≠ c, we have f (x) – f (c) = ( ) ( ) ( ) f x f c x c x c − − − Therefore lim[ ( ) ( )] x c f x f c → − = ( ) ( ) lim ( ) x c f x f c x c x c → −   −   −   or lim[ ( )] lim[ ( )] x c x c f x f c → −→ = ( ) ( ) lim
1
2035-2038
Proof Since f is differentiable at c, we have ( ) ( ) lim ( ) x c f x f c f c x c → − = ′ − But for x ≠ c, we have f (x) – f (c) = ( ) ( ) ( ) f x f c x c x c − − − Therefore lim[ ( ) ( )] x c f x f c → − = ( ) ( ) lim ( ) x c f x f c x c x c → −   −   −   or lim[ ( )] lim[ ( )] x c x c f x f c → −→ = ( ) ( ) lim lim [( )] x c x c f x f c x c x c → → −   −   −   = f′(c)
1
2036-2039
( ) f x f c x c x c − − − Therefore lim[ ( ) ( )] x c f x f c → − = ( ) ( ) lim ( ) x c f x f c x c x c → −   −   −   or lim[ ( )] lim[ ( )] x c x c f x f c → −→ = ( ) ( ) lim lim [( )] x c x c f x f c x c x c → → −   −   −   = f′(c) 0 = 0 or lim ( ) x c f x → = f (c) Hence f is continuous at x = c
1
2037-2040
( ) x c f x f c x c x c → −   −   −   or lim[ ( )] lim[ ( )] x c x c f x f c → −→ = ( ) ( ) lim lim [( )] x c x c f x f c x c x c → → −   −   −   = f′(c) 0 = 0 or lim ( ) x c f x → = f (c) Hence f is continuous at x = c Corollary 1 Every differentiable function is continuous
1
2038-2041
lim [( )] x c x c f x f c x c x c → → −   −   −   = f′(c) 0 = 0 or lim ( ) x c f x → = f (c) Hence f is continuous at x = c Corollary 1 Every differentiable function is continuous We remark that the converse of the above statement is not true
1
2039-2042
0 = 0 or lim ( ) x c f x → = f (c) Hence f is continuous at x = c Corollary 1 Every differentiable function is continuous We remark that the converse of the above statement is not true Indeed we have seen that the function defined by f(x) = |x | is a continuous function
1
2040-2043
Corollary 1 Every differentiable function is continuous We remark that the converse of the above statement is not true Indeed we have seen that the function defined by f(x) = |x | is a continuous function Consider the left hand limit 0– (0 ) (0) lim 1 h f h f h h h → + − =− = − The right hand limit 0 (0 ) (0) lim 1 h f h f h h h + → + − = = Since the above left and right hand limits at 0 are not equal, 0 (0 ) (0) lim h f h f h → + − does not exist and hence f is not differentiable at 0
1
2041-2044
We remark that the converse of the above statement is not true Indeed we have seen that the function defined by f(x) = |x | is a continuous function Consider the left hand limit 0– (0 ) (0) lim 1 h f h f h h h → + − =− = − The right hand limit 0 (0 ) (0) lim 1 h f h f h h h + → + − = = Since the above left and right hand limits at 0 are not equal, 0 (0 ) (0) lim h f h f h → + − does not exist and hence f is not differentiable at 0 Thus f is not a differentiable function
1
2042-2045
Indeed we have seen that the function defined by f(x) = |x | is a continuous function Consider the left hand limit 0– (0 ) (0) lim 1 h f h f h h h → + − =− = − The right hand limit 0 (0 ) (0) lim 1 h f h f h h h + → + − = = Since the above left and right hand limits at 0 are not equal, 0 (0 ) (0) lim h f h f h → + − does not exist and hence f is not differentiable at 0 Thus f is not a differentiable function 5
1
2043-2046
Consider the left hand limit 0– (0 ) (0) lim 1 h f h f h h h → + − =− = − The right hand limit 0 (0 ) (0) lim 1 h f h f h h h + → + − = = Since the above left and right hand limits at 0 are not equal, 0 (0 ) (0) lim h f h f h → + − does not exist and hence f is not differentiable at 0 Thus f is not a differentiable function 5 3
1
2044-2047
Thus f is not a differentiable function 5 3 1 Derivatives of composite functions To study derivative of composite functions, we start with an illustrative example
1
2045-2048
5 3 1 Derivatives of composite functions To study derivative of composite functions, we start with an illustrative example Say, we want to find the derivative of f, where f (x) = (2x + 1)3 Rationalised 2023-24 CONTINUITY AND DIFFERENTIABILITY 121 One way is to expand (2x + 1)3 using binomial theorem and find the derivative as a polynomial function as illustrated below
1
2046-2049
3 1 Derivatives of composite functions To study derivative of composite functions, we start with an illustrative example Say, we want to find the derivative of f, where f (x) = (2x + 1)3 Rationalised 2023-24 CONTINUITY AND DIFFERENTIABILITY 121 One way is to expand (2x + 1)3 using binomial theorem and find the derivative as a polynomial function as illustrated below ( ) dxd f x = 3 (2 1) d x dx   +   = 3 2 (8 12 6 1) d x x x dx + + + = 24x2 + 24x + 6 = 6 (2x + 1)2 Now, observe that f (x) = (h o g) (x) where g(x) = 2x + 1 and h(x) = x3
1
2047-2050
1 Derivatives of composite functions To study derivative of composite functions, we start with an illustrative example Say, we want to find the derivative of f, where f (x) = (2x + 1)3 Rationalised 2023-24 CONTINUITY AND DIFFERENTIABILITY 121 One way is to expand (2x + 1)3 using binomial theorem and find the derivative as a polynomial function as illustrated below ( ) dxd f x = 3 (2 1) d x dx   +   = 3 2 (8 12 6 1) d x x x dx + + + = 24x2 + 24x + 6 = 6 (2x + 1)2 Now, observe that f (x) = (h o g) (x) where g(x) = 2x + 1 and h(x) = x3 Put t = g(x) = 2x + 1
1
2048-2051
Say, we want to find the derivative of f, where f (x) = (2x + 1)3 Rationalised 2023-24 CONTINUITY AND DIFFERENTIABILITY 121 One way is to expand (2x + 1)3 using binomial theorem and find the derivative as a polynomial function as illustrated below ( ) dxd f x = 3 (2 1) d x dx   +   = 3 2 (8 12 6 1) d x x x dx + + + = 24x2 + 24x + 6 = 6 (2x + 1)2 Now, observe that f (x) = (h o g) (x) where g(x) = 2x + 1 and h(x) = x3 Put t = g(x) = 2x + 1 Then f(x) = h(t) = t3
1
2049-2052
( ) dxd f x = 3 (2 1) d x dx   +   = 3 2 (8 12 6 1) d x x x dx + + + = 24x2 + 24x + 6 = 6 (2x + 1)2 Now, observe that f (x) = (h o g) (x) where g(x) = 2x + 1 and h(x) = x3 Put t = g(x) = 2x + 1 Then f(x) = h(t) = t3 Thus df dx = 6 (2x + 1)2 = 3(2x + 1)2
1
2050-2053
Put t = g(x) = 2x + 1 Then f(x) = h(t) = t3 Thus df dx = 6 (2x + 1)2 = 3(2x + 1)2 2 = 3t2
1
2051-2054
Then f(x) = h(t) = t3 Thus df dx = 6 (2x + 1)2 = 3(2x + 1)2 2 = 3t2 2 = dh dt dt dx ⋅ The advantage with such observation is that it simplifies the calculation in finding the derivative of, say, (2x + 1)100
1
2052-2055
Thus df dx = 6 (2x + 1)2 = 3(2x + 1)2 2 = 3t2 2 = dh dt dt dx ⋅ The advantage with such observation is that it simplifies the calculation in finding the derivative of, say, (2x + 1)100 We may formalise this observation in the following theorem called the chain rule
1
2053-2056
2 = 3t2 2 = dh dt dt dx ⋅ The advantage with such observation is that it simplifies the calculation in finding the derivative of, say, (2x + 1)100 We may formalise this observation in the following theorem called the chain rule Theorem 4 (Chain Rule) Let f be a real valued function which is a composite of two functions u and v; i
1
2054-2057
2 = dh dt dt dx ⋅ The advantage with such observation is that it simplifies the calculation in finding the derivative of, say, (2x + 1)100 We may formalise this observation in the following theorem called the chain rule Theorem 4 (Chain Rule) Let f be a real valued function which is a composite of two functions u and v; i e
1
2055-2058
We may formalise this observation in the following theorem called the chain rule Theorem 4 (Chain Rule) Let f be a real valued function which is a composite of two functions u and v; i e , f = v o u
1
2056-2059
Theorem 4 (Chain Rule) Let f be a real valued function which is a composite of two functions u and v; i e , f = v o u Suppose t = u(x) and if both dt dx and dv dt exist, we have df dv dt dx =dt dx ⋅ We skip the proof of this theorem
1
2057-2060
e , f = v o u Suppose t = u(x) and if both dt dx and dv dt exist, we have df dv dt dx =dt dx ⋅ We skip the proof of this theorem Chain rule may be extended as follows
1
2058-2061
, f = v o u Suppose t = u(x) and if both dt dx and dv dt exist, we have df dv dt dx =dt dx ⋅ We skip the proof of this theorem Chain rule may be extended as follows Suppose f is a real valued function which is a composite of three functions u, v and w; i
1
2059-2062
Suppose t = u(x) and if both dt dx and dv dt exist, we have df dv dt dx =dt dx ⋅ We skip the proof of this theorem Chain rule may be extended as follows Suppose f is a real valued function which is a composite of three functions u, v and w; i e
1
2060-2063
Chain rule may be extended as follows Suppose f is a real valued function which is a composite of three functions u, v and w; i e , f = (w o u) o v
1
2061-2064
Suppose f is a real valued function which is a composite of three functions u, v and w; i e , f = (w o u) o v If t = v (x) and s = u (t), then ( o ) df d w u dt dw ds dt dx dt dx ds dt dx = ⋅ = ⋅ ⋅ provided all the derivatives in the statement exist
1
2062-2065
e , f = (w o u) o v If t = v (x) and s = u (t), then ( o ) df d w u dt dw ds dt dx dt dx ds dt dx = ⋅ = ⋅ ⋅ provided all the derivatives in the statement exist Reader is invited to formulate chain rule for composite of more functions
1
2063-2066
, f = (w o u) o v If t = v (x) and s = u (t), then ( o ) df d w u dt dw ds dt dx dt dx ds dt dx = ⋅ = ⋅ ⋅ provided all the derivatives in the statement exist Reader is invited to formulate chain rule for composite of more functions Example 21 Find the derivative of the function given by f(x) = sin (x2)
1
2064-2067
If t = v (x) and s = u (t), then ( o ) df d w u dt dw ds dt dx dt dx ds dt dx = ⋅ = ⋅ ⋅ provided all the derivatives in the statement exist Reader is invited to formulate chain rule for composite of more functions Example 21 Find the derivative of the function given by f(x) = sin (x2) Solution Observe that the given function is a composite of two functions
1
2065-2068
Reader is invited to formulate chain rule for composite of more functions Example 21 Find the derivative of the function given by f(x) = sin (x2) Solution Observe that the given function is a composite of two functions Indeed, if t = u(x) = x2 and v(t) = sin t, then f (x) = (v o u) (x) = v(u(x)) = v(x2) = sin x2 Rationalised 2023-24 MATHEMATICS 122 Put t = u(x) = x2
1
2066-2069
Example 21 Find the derivative of the function given by f(x) = sin (x2) Solution Observe that the given function is a composite of two functions Indeed, if t = u(x) = x2 and v(t) = sin t, then f (x) = (v o u) (x) = v(u(x)) = v(x2) = sin x2 Rationalised 2023-24 MATHEMATICS 122 Put t = u(x) = x2 Observe that cos dv t dt = and 2 dt dx =x exist
1
2067-2070
Solution Observe that the given function is a composite of two functions Indeed, if t = u(x) = x2 and v(t) = sin t, then f (x) = (v o u) (x) = v(u(x)) = v(x2) = sin x2 Rationalised 2023-24 MATHEMATICS 122 Put t = u(x) = x2 Observe that cos dv t dt = and 2 dt dx =x exist Hence, by chain rule df dx = cos 2 dv dt t x dt ⋅dx = ⋅ It is normal practice to express the final result only in terms of x
1
2068-2071
Indeed, if t = u(x) = x2 and v(t) = sin t, then f (x) = (v o u) (x) = v(u(x)) = v(x2) = sin x2 Rationalised 2023-24 MATHEMATICS 122 Put t = u(x) = x2 Observe that cos dv t dt = and 2 dt dx =x exist Hence, by chain rule df dx = cos 2 dv dt t x dt ⋅dx = ⋅ It is normal practice to express the final result only in terms of x Thus df dx = 2 cos 2 2 cos t x x x ⋅ = EXERCISE 5
1
2069-2072
Observe that cos dv t dt = and 2 dt dx =x exist Hence, by chain rule df dx = cos 2 dv dt t x dt ⋅dx = ⋅ It is normal practice to express the final result only in terms of x Thus df dx = 2 cos 2 2 cos t x x x ⋅ = EXERCISE 5 2 Differentiate the functions with respect to x in Exercises 1 to 8
1
2070-2073
Hence, by chain rule df dx = cos 2 dv dt t x dt ⋅dx = ⋅ It is normal practice to express the final result only in terms of x Thus df dx = 2 cos 2 2 cos t x x x ⋅ = EXERCISE 5 2 Differentiate the functions with respect to x in Exercises 1 to 8 1
1
2071-2074
Thus df dx = 2 cos 2 2 cos t x x x ⋅ = EXERCISE 5 2 Differentiate the functions with respect to x in Exercises 1 to 8 1 sin (x2 + 5) 2
1
2072-2075
2 Differentiate the functions with respect to x in Exercises 1 to 8 1 sin (x2 + 5) 2 cos (sin x) 3
1
2073-2076
1 sin (x2 + 5) 2 cos (sin x) 3 sin (ax + b) 4
1
2074-2077
sin (x2 + 5) 2 cos (sin x) 3 sin (ax + b) 4 sec (tan ( x )) 5
1
2075-2078
cos (sin x) 3 sin (ax + b) 4 sec (tan ( x )) 5 sin ( ) cos ( ) ax b cx d ++ 6
1
2076-2079
sin (ax + b) 4 sec (tan ( x )) 5 sin ( ) cos ( ) ax b cx d ++ 6 cos x3
1
2077-2080
sec (tan ( x )) 5 sin ( ) cos ( ) ax b cx d ++ 6 cos x3 sin2 (x5) 7
1
2078-2081
sin ( ) cos ( ) ax b cx d ++ 6 cos x3 sin2 (x5) 7 ( 2 cot x2) 8
1
2079-2082
cos x3 sin2 (x5) 7 ( 2 cot x2) 8 ( ) cos x 9
1
2080-2083
sin2 (x5) 7 ( 2 cot x2) 8 ( ) cos x 9 Prove that the function f given by f (x) = |x – 1|, x ∈ R is not differentiable at x = 1
1
2081-2084
( 2 cot x2) 8 ( ) cos x 9 Prove that the function f given by f (x) = |x – 1|, x ∈ R is not differentiable at x = 1 10
1
2082-2085
( ) cos x 9 Prove that the function f given by f (x) = |x – 1|, x ∈ R is not differentiable at x = 1 10 Prove that the greatest integer function defined by f (x) = [x], 0 < x < 3 is not differentiable at x = 1 and x = 2
1
2083-2086
Prove that the function f given by f (x) = |x – 1|, x ∈ R is not differentiable at x = 1 10 Prove that the greatest integer function defined by f (x) = [x], 0 < x < 3 is not differentiable at x = 1 and x = 2 5
1
2084-2087
10 Prove that the greatest integer function defined by f (x) = [x], 0 < x < 3 is not differentiable at x = 1 and x = 2 5 3
1
2085-2088
Prove that the greatest integer function defined by f (x) = [x], 0 < x < 3 is not differentiable at x = 1 and x = 2 5 3 2 Derivatives of implicit functions Until now we have been differentiating various functions given in the form y = f(x)
1
2086-2089
5 3 2 Derivatives of implicit functions Until now we have been differentiating various functions given in the form y = f(x) But it is not necessary that functions are always expressed in this form
1
2087-2090
3 2 Derivatives of implicit functions Until now we have been differentiating various functions given in the form y = f(x) But it is not necessary that functions are always expressed in this form For example, consider one of the following relationships between x and y: x – y – π = 0 x + sin xy – y = 0 In the first case, we can solve for y and rewrite the relationship as y = x – π
1
2088-2091
2 Derivatives of implicit functions Until now we have been differentiating various functions given in the form y = f(x) But it is not necessary that functions are always expressed in this form For example, consider one of the following relationships between x and y: x – y – π = 0 x + sin xy – y = 0 In the first case, we can solve for y and rewrite the relationship as y = x – π In the second case, it does not seem that there is an easy way to solve for y
1
2089-2092
But it is not necessary that functions are always expressed in this form For example, consider one of the following relationships between x and y: x – y – π = 0 x + sin xy – y = 0 In the first case, we can solve for y and rewrite the relationship as y = x – π In the second case, it does not seem that there is an easy way to solve for y Nevertheless, there is no doubt about the dependence of y on x in either of the cases
1
2090-2093
For example, consider one of the following relationships between x and y: x – y – π = 0 x + sin xy – y = 0 In the first case, we can solve for y and rewrite the relationship as y = x – π In the second case, it does not seem that there is an easy way to solve for y Nevertheless, there is no doubt about the dependence of y on x in either of the cases When a relationship between x and y is expressed in a way that it is easy to solve for y and write y = f(x), we say that y is given as an explicit function of x
1
2091-2094
In the second case, it does not seem that there is an easy way to solve for y Nevertheless, there is no doubt about the dependence of y on x in either of the cases When a relationship between x and y is expressed in a way that it is easy to solve for y and write y = f(x), we say that y is given as an explicit function of x In the latter case it Rationalised 2023-24 CONTINUITY AND DIFFERENTIABILITY 123 is implicit that y is a function of x and we say that the relationship of the second type, above, gives function implicitly
1
2092-2095
Nevertheless, there is no doubt about the dependence of y on x in either of the cases When a relationship between x and y is expressed in a way that it is easy to solve for y and write y = f(x), we say that y is given as an explicit function of x In the latter case it Rationalised 2023-24 CONTINUITY AND DIFFERENTIABILITY 123 is implicit that y is a function of x and we say that the relationship of the second type, above, gives function implicitly In this subsection, we learn to differentiate implicit functions
1
2093-2096
When a relationship between x and y is expressed in a way that it is easy to solve for y and write y = f(x), we say that y is given as an explicit function of x In the latter case it Rationalised 2023-24 CONTINUITY AND DIFFERENTIABILITY 123 is implicit that y is a function of x and we say that the relationship of the second type, above, gives function implicitly In this subsection, we learn to differentiate implicit functions Example 22 Find dy dx if x – y = π
1
2094-2097
In the latter case it Rationalised 2023-24 CONTINUITY AND DIFFERENTIABILITY 123 is implicit that y is a function of x and we say that the relationship of the second type, above, gives function implicitly In this subsection, we learn to differentiate implicit functions Example 22 Find dy dx if x – y = π Solution One way is to solve for y and rewrite the above as y = x – π But then dy dx = 1 Alternatively, directly differentiating the relationship w
1
2095-2098
In this subsection, we learn to differentiate implicit functions Example 22 Find dy dx if x – y = π Solution One way is to solve for y and rewrite the above as y = x – π But then dy dx = 1 Alternatively, directly differentiating the relationship w r
1
2096-2099
Example 22 Find dy dx if x – y = π Solution One way is to solve for y and rewrite the above as y = x – π But then dy dx = 1 Alternatively, directly differentiating the relationship w r t
1
2097-2100
Solution One way is to solve for y and rewrite the above as y = x – π But then dy dx = 1 Alternatively, directly differentiating the relationship w r t , x, we have ( ) d x y dx − = d dx π Recall that d dx π means to differentiate the constant function taking value π everywhere w
1
2098-2101
r t , x, we have ( ) d x y dx − = d dx π Recall that d dx π means to differentiate the constant function taking value π everywhere w r
1
2099-2102
t , x, we have ( ) d x y dx − = d dx π Recall that d dx π means to differentiate the constant function taking value π everywhere w r t
1
2100-2103
, x, we have ( ) d x y dx − = d dx π Recall that d dx π means to differentiate the constant function taking value π everywhere w r t , x
1
2101-2104
r t , x Thus ( ) ( ) d d x y dx −dx = 0 which implies that dy dx = 1 dx dx = Example 23 Find dy dx , if y + sin y = cos x
1
2102-2105
t , x Thus ( ) ( ) d d x y dx −dx = 0 which implies that dy dx = 1 dx dx = Example 23 Find dy dx , if y + sin y = cos x Solution We differentiate the relationship directly with respect to x, i
1
2103-2106
, x Thus ( ) ( ) d d x y dx −dx = 0 which implies that dy dx = 1 dx dx = Example 23 Find dy dx , if y + sin y = cos x Solution We differentiate the relationship directly with respect to x, i e
1
2104-2107
Thus ( ) ( ) d d x y dx −dx = 0 which implies that dy dx = 1 dx dx = Example 23 Find dy dx , if y + sin y = cos x Solution We differentiate the relationship directly with respect to x, i e , (sin ) dy d y dx +dx = d(cos ) x dx which implies using chain rule cos dy ydy dx dx + ⋅ = – sin x This gives dy dx = sin 1 cos x y − + where y ≠ (2n + 1) π Rationalised 2023-24 MATHEMATICS 124 5
1
2105-2108
Solution We differentiate the relationship directly with respect to x, i e , (sin ) dy d y dx +dx = d(cos ) x dx which implies using chain rule cos dy ydy dx dx + ⋅ = – sin x This gives dy dx = sin 1 cos x y − + where y ≠ (2n + 1) π Rationalised 2023-24 MATHEMATICS 124 5 3
1
2106-2109
e , (sin ) dy d y dx +dx = d(cos ) x dx which implies using chain rule cos dy ydy dx dx + ⋅ = – sin x This gives dy dx = sin 1 cos x y − + where y ≠ (2n + 1) π Rationalised 2023-24 MATHEMATICS 124 5 3 3 Derivatives of inverse trigonometric functions We remark that inverse trigonometric functions are continuous functions, but we will not prove this
1
2107-2110
, (sin ) dy d y dx +dx = d(cos ) x dx which implies using chain rule cos dy ydy dx dx + ⋅ = – sin x This gives dy dx = sin 1 cos x y − + where y ≠ (2n + 1) π Rationalised 2023-24 MATHEMATICS 124 5 3 3 Derivatives of inverse trigonometric functions We remark that inverse trigonometric functions are continuous functions, but we will not prove this Now we use chain rule to find derivatives of these functions
1
2108-2111
3 3 Derivatives of inverse trigonometric functions We remark that inverse trigonometric functions are continuous functions, but we will not prove this Now we use chain rule to find derivatives of these functions Example 24 Find the derivative of f given by f(x) = sin–1 x assuming it exists
1
2109-2112
3 Derivatives of inverse trigonometric functions We remark that inverse trigonometric functions are continuous functions, but we will not prove this Now we use chain rule to find derivatives of these functions Example 24 Find the derivative of f given by f(x) = sin–1 x assuming it exists Solution Let y = sin–1 x
1
2110-2113
Now we use chain rule to find derivatives of these functions Example 24 Find the derivative of f given by f(x) = sin–1 x assuming it exists Solution Let y = sin–1 x Then, x = sin y
1
2111-2114
Example 24 Find the derivative of f given by f(x) = sin–1 x assuming it exists Solution Let y = sin–1 x Then, x = sin y Differentiating both sides w
1
2112-2115
Solution Let y = sin–1 x Then, x = sin y Differentiating both sides w r
1
2113-2116
Then, x = sin y Differentiating both sides w r t
1
2114-2117
Differentiating both sides w r t x, we get 1 = cos y dy dx which implies that dy dx = 1 1 1 cos cos(sin ) y x − = Observe that this is defined only for cos y ≠ 0, i
1
2115-2118
r t x, we get 1 = cos y dy dx which implies that dy dx = 1 1 1 cos cos(sin ) y x − = Observe that this is defined only for cos y ≠ 0, i e
1
2116-2119
t x, we get 1 = cos y dy dx which implies that dy dx = 1 1 1 cos cos(sin ) y x − = Observe that this is defined only for cos y ≠ 0, i e , sin–1 x ≠ , 2 2 −π π , i
1
2117-2120
x, we get 1 = cos y dy dx which implies that dy dx = 1 1 1 cos cos(sin ) y x − = Observe that this is defined only for cos y ≠ 0, i e , sin–1 x ≠ , 2 2 −π π , i e