Calculate the derivative of y = cos (7x³). (Use symbolic notation and fractions where needed.)

Calculus: Early Transcendentals
8th Edition
ISBN:9781285741550
Author:James Stewart
Publisher:James Stewart
Chapter1: Functions And Models
Section: Chapter Questions
Problem 1RCC: (a) What is a function? What are its domain and range? (b) What is the graph of a function? (c) How...
Question
**Topic: Differentiation of Trigonometric Functions**

**Problem Statement:**

Calculate the derivative of \( y = \cos(7x^3) \).

(Use symbolic notation and fractions where needed.)

\( y' = \) 

**Solution:**

To solve this problem, we'll need to use the chain rule for differentiation. The chain rule states that if you have a composite function \( f(g(x)) \), then the derivative is \( f'(g(x)) \cdot g'(x) \).

1. Given the function \( y = \cos(7x^3) \), identify the outer and inner functions:
   - Outer function: \( f(u) = \cos(u) \)
   - Inner function: \( u = 7x^3 \)

2. Find the derivative of the outer function:
   \( f'(u) = -\sin(u) \)

3. Find the derivative of the inner function:
   \( u = 7x^3 \)
   \( u' = 21x^2 \)

4. Apply the chain rule:
   \[
   y' = f'(u) \cdot u'
   \]
   \[
   y' = -\sin(7x^3) \cdot 21x^2
   \]

Simplify the expression:
\[
y' = -21x^2 \sin(7x^3)
\]

Thus, the derivative of \( y = \cos(7x^3) \) is:
\[
y' = -21x^2 \sin(7x^3)
\]
Transcribed Image Text:**Topic: Differentiation of Trigonometric Functions** **Problem Statement:** Calculate the derivative of \( y = \cos(7x^3) \). (Use symbolic notation and fractions where needed.) \( y' = \) **Solution:** To solve this problem, we'll need to use the chain rule for differentiation. The chain rule states that if you have a composite function \( f(g(x)) \), then the derivative is \( f'(g(x)) \cdot g'(x) \). 1. Given the function \( y = \cos(7x^3) \), identify the outer and inner functions: - Outer function: \( f(u) = \cos(u) \) - Inner function: \( u = 7x^3 \) 2. Find the derivative of the outer function: \( f'(u) = -\sin(u) \) 3. Find the derivative of the inner function: \( u = 7x^3 \) \( u' = 21x^2 \) 4. Apply the chain rule: \[ y' = f'(u) \cdot u' \] \[ y' = -\sin(7x^3) \cdot 21x^2 \] Simplify the expression: \[ y' = -21x^2 \sin(7x^3) \] Thus, the derivative of \( y = \cos(7x^3) \) is: \[ y' = -21x^2 \sin(7x^3) \]
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