f'(x) = f(x) = Find a formula for f'(x). Note: f(x) is differentiable at x = -1, but is NOT differentiable at x = 1. Can you see why that is so? if x < -1 if if x > 1 - 1 1

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Author:James Stewart
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Chapter1: Functions And Models
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### Differentiation of Piecewise Functions

We are given a piecewise function \( f(x) \) defined as follows:

\[ f(x) = 
  \begin{cases} 
   -(12x + 6) & \text{if } x < -1 \\
   6x^2 & \text{if } -1 \le x \le 1 \\
   6x & \text{if } x > 1 
  \end{cases}
\]

#### Objective
Find a formula for the derivative of the function \( f'(x) \).

#### Note
\( f(x) \) is differentiable at \( x = -1 \), but it is NOT differentiable at \( x = 1 \). Investigate why this differentiation is not possible at \( x = 1 \).

#### Solution
To determine the derivative for each piece:

1. For \( x < -1 \):
   \[
   f(x) = -(12x + 6) \\
   f'(x) = \frac{d}{dx} [-(12x + 6)] = -12
   \]

2. For \( -1 \le x \le 1 \):
   \[
   f(x) = 6x^2 \\
   f'(x) = \frac{d}{dx} [6x^2] = 12x
   \]

3. For \( x > 1 \):
   \[
   f(x) = 6x \\
   f'(x) = \frac{d}{dx} [6x] = 6
   \]

Thus, the derivative \( f'(x) \) is given by:

\[ f'(x) = 
  \begin{cases} 
   -12 & \text{if } x < -1 \\
   12x & \text{if } -1 \le x < 1 \\
   6 & \text{if } x > 1 
  \end{cases}
\]

### Explanation
\( f(x) \) is differentiable at \( x = -1 \) because both the function itself and its derivative are continuous at this point. However, at \( x = 1 \), although \( f(x) \) is continuous, the derivatives from the left (\(12x\)) and the right (\(
Transcribed Image Text:### Differentiation of Piecewise Functions We are given a piecewise function \( f(x) \) defined as follows: \[ f(x) = \begin{cases} -(12x + 6) & \text{if } x < -1 \\ 6x^2 & \text{if } -1 \le x \le 1 \\ 6x & \text{if } x > 1 \end{cases} \] #### Objective Find a formula for the derivative of the function \( f'(x) \). #### Note \( f(x) \) is differentiable at \( x = -1 \), but it is NOT differentiable at \( x = 1 \). Investigate why this differentiation is not possible at \( x = 1 \). #### Solution To determine the derivative for each piece: 1. For \( x < -1 \): \[ f(x) = -(12x + 6) \\ f'(x) = \frac{d}{dx} [-(12x + 6)] = -12 \] 2. For \( -1 \le x \le 1 \): \[ f(x) = 6x^2 \\ f'(x) = \frac{d}{dx} [6x^2] = 12x \] 3. For \( x > 1 \): \[ f(x) = 6x \\ f'(x) = \frac{d}{dx} [6x] = 6 \] Thus, the derivative \( f'(x) \) is given by: \[ f'(x) = \begin{cases} -12 & \text{if } x < -1 \\ 12x & \text{if } -1 \le x < 1 \\ 6 & \text{if } x > 1 \end{cases} \] ### Explanation \( f(x) \) is differentiable at \( x = -1 \) because both the function itself and its derivative are continuous at this point. However, at \( x = 1 \), although \( f(x) \) is continuous, the derivatives from the left (\(12x\)) and the right (\(
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