Find the second derivative of the function. f(x) = 5(2 − 7x)ª

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
**Calculating the Second Derivative**

To find the second derivative of the function:

\[ f(x) = 5(2 - 7x)^4 \]

Step 1: Find the first derivative \( f'(x) \).

Use the chain rule for differentiation. Let \( u = 2 - 7x \). Then, \( f(x) = 5u^4 \) and 

\[ \frac{d}{dx}[5u^4] = 5 \cdot 4u^3 \cdot \frac{du}{dx} \]

First, differentiate \( u = 2 - 7x \). The derivative of \( u \) with respect to \( x \) is:

\[ \frac{du}{dx} = \frac{d}{dx}(2 - 7x) = -7 \]

Hence,

\[ f'(x) = 5 \cdot 4(2 - 7x)^3 \cdot (-7) = -140(2 - 7x)^3 \]

Step 2: Find the second derivative \( f''(x) \).

To find the second derivative, differentiate \( f'(x) \) with respect to \( x \):

\[ f'(x) = -140(2 - 7x)^3 \]

Again, applying the chain rule, let \( u = 2 - 7x \), then:

\[ \frac{d}{dx}[-140u^3] = -140 \cdot 3u^2 \cdot \frac{du}{dx} \]

We already know \( \frac{du}{dx} = -7 \), hence,

\[ f''(x) = -140 \cdot 3(2 - 7x)^2 \cdot (-7) = 2940(2 - 7x)^2 \]

Thus, the second derivative of the function is:

\[ f''(x) = 2940(2 - 7x)^2 \]
Transcribed Image Text:**Calculating the Second Derivative** To find the second derivative of the function: \[ f(x) = 5(2 - 7x)^4 \] Step 1: Find the first derivative \( f'(x) \). Use the chain rule for differentiation. Let \( u = 2 - 7x \). Then, \( f(x) = 5u^4 \) and \[ \frac{d}{dx}[5u^4] = 5 \cdot 4u^3 \cdot \frac{du}{dx} \] First, differentiate \( u = 2 - 7x \). The derivative of \( u \) with respect to \( x \) is: \[ \frac{du}{dx} = \frac{d}{dx}(2 - 7x) = -7 \] Hence, \[ f'(x) = 5 \cdot 4(2 - 7x)^3 \cdot (-7) = -140(2 - 7x)^3 \] Step 2: Find the second derivative \( f''(x) \). To find the second derivative, differentiate \( f'(x) \) with respect to \( x \): \[ f'(x) = -140(2 - 7x)^3 \] Again, applying the chain rule, let \( u = 2 - 7x \), then: \[ \frac{d}{dx}[-140u^3] = -140 \cdot 3u^2 \cdot \frac{du}{dx} \] We already know \( \frac{du}{dx} = -7 \), hence, \[ f''(x) = -140 \cdot 3(2 - 7x)^2 \cdot (-7) = 2940(2 - 7x)^2 \] Thus, the second derivative of the function is: \[ f''(x) = 2940(2 - 7x)^2 \]
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