Quiz:Chain rule for differentiation: Difference between revisions

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==Formulas==
==Formulas==
General difficulty level of questions in this section: College level (unless otherwise specified).


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- <math>ab^{n - 1}</math>
- <math>ab^{n - 1}</math>
+ <math>b^n</math>
+ <math>b^n</math>
|| The chain rule gives the derivative as a product of <math>n</math> terms, each of which is of the form <math>f'<math> applied to <math>k</math> iterates of <math>f</math>, with <math>k</math> varying from <math>0</math> to <math>n - 1</math>. Evaluating at <math>a</math> and using <math>f'(a) = a</math>, each term simplifies to <math>f'(a)</math> and hence to <math>b</math>. As there are <math>n</math> such terms, the product is <math>b^n</math>. Note that <math>n \ge 3</math> is not necessary (this reasoning works for <math>n = 1</math> and <math>n = 2</math> as well). That condition was added primarily to dissuade people from using <math>n = 1</math> or <math>n = 2</math> to figure out the correct answer by a process of elimination.
|| The chain rule gives the derivative as a product of <math>n</math> terms, each of which is of the form <math>f'</math> applied to <math>k</math> iterates of <math>f</math>, with <math>k</math> varying from <math>0</math> to <math>n - 1</math>. Evaluating at <math>a</math> and using <math>f'(a) = a</math>, each term simplifies to <math>f'(a)</math> and hence to <math>b</math>. As there are <math>n</math> such terms, the product is <math>b^n</math>. Note that <math>n \ge 3</math> is not necessary (this reasoning works for <math>n = 1</math> and <math>n = 2</math> as well). That condition was added primarily to dissuade people from using <math>n = 1</math> or <math>n = 2</math> to figure out the correct answer by a process of elimination.


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Latest revision as of 21:40, 18 March 2024

See chain rule for differentiation and chain rule for higher derivatives for background information.

See Quiz:Differentiation rules for a quiz on all the differentiation rules together.

Formulas

General difficulty level of questions in this section: College level (unless otherwise specified).

1 Suppose f and g are both twice differentiable functions everywhere on R. Which of the following is the correct formula for (fg), the second derivative of the composite of two functions?

(fg)g
(fg)(fg)g
(fg)(fg)(fg)
(fg)(g)2+(fg)g
(fg)(fg)+(fg)

2 Suppose f1,f2,f3 are everywhere differentiable functions from R to R. What is the derivative (f1f2f3) where denotes the composite of two functions? In other words, (f1f2f3)(x):=f1(f2(f3(x))).

(f1f2f3)(f2f3)f3
(f1f2f3)(f2f3)f3
(f1f2f3)(f2f3)f3
(f1f2f3)(f2f3)f3
f1f2f3

3 Suppose f is a differentiable function from R to R and a,bR are such that f(a)=a and f(a)=b. What is the value of (fff)(a), where denotes the composite of two functions and f occurs n times in the expression, with n3?

an
an1b
an1b+abn1
abn1
bn