Math Problem Statement

Consider the following function. f(x) = 4 − x2/3 Find f(−8) and f(8).

f(−8)

f(8)

Find all values c in (−8, 8) such that f '(c) = 0. (Enter your answers as a comma-separated list. If an answer does not exist, enter DNE.) c =
Based off of this information, what conclusions can be made about Rolle's Theorem?

This contradicts Rolle's Theorem, since f is differentiable, f(−8) = f(8), and f '(c) = 0 exists, but c is not in (−8, 8). This does not contradict Rolle's Theorem, since f '(0) = 0, and 0 is in the interval (−8, 8).
This contradicts Rolle's Theorem, since f(−8) = f(8), there should exist a number c in (−8, 8) such that f '(c) = 0. This does not contradict Rolle's Theorem, since f '(0) does not exist, and so f is not differentiable on (−8, 8). Nothing can be concluded.

Solution

Let's solve this step-by-step.

Step 1: Evaluate f(8)f(-8) and f(8)f(8)

The given function is:

f(x)=4x2/3f(x) = 4 - x^{2/3}

Now, substitute x=8x = -8 and x=8x = 8 to find f(8)f(-8) and f(8)f(8).

For f(8)f(-8):

f(8)=4(8)2/3f(-8) = 4 - (-8)^{2/3}

The cube root of 8-8 is 2-2, and squaring 2-2 gives 44. So,

f(8)=44=0f(-8) = 4 - 4 = 0

For f(8)f(8):

f(8)=4(8)2/3f(8) = 4 - (8)^{2/3}

The cube root of 88 is 22, and squaring 22 gives 44. So,

f(8)=44=0f(8) = 4 - 4 = 0

Thus, f(8)=0f(-8) = 0 and f(8)=0f(8) = 0.

Step 2: Find f(x)f'(x)

Now, we differentiate the function f(x)=4x2/3f(x) = 4 - x^{2/3}.

Using the power rule for differentiation:

f(x)=ddx(4x2/3)=023x1/3=23x1/3f'(x) = \frac{d}{dx}\left(4 - x^{2/3}\right) = 0 - \frac{2}{3}x^{-1/3} = -\frac{2}{3}x^{-1/3}

So,

f(x)=231x3f'(x) = -\frac{2}{3} \cdot \frac{1}{\sqrt[3]{x}}

Step 3: Find cc such that f(c)=0f'(c) = 0

Set f(x)=0f'(x) = 0:

231x3=0-\frac{2}{3} \cdot \frac{1}{\sqrt[3]{x}} = 0

For this equation to hold, there is no value of xx that makes 231x3=0-\frac{2}{3} \cdot \frac{1}{\sqrt[3]{x}} = 0. This implies that there is no cc in the interval (8,8)(-8, 8) such that f(c)=0f'(c) = 0.

Therefore, the answer for cc is:

c=DNE (Does Not Exist)c = \text{DNE (Does Not Exist)}

Step 4: Rolle's Theorem

Rolle's Theorem states that if a function ff is continuous on the closed interval [a,b][a, b], differentiable on the open interval (a,b)(a, b), and f(a)=f(b)f(a) = f(b), then there exists at least one c(a,b)c \in (a, b) such that f(c)=0f'(c) = 0.

In this case:

  • f(8)=f(8)=0f(-8) = f(8) = 0, so the first condition is satisfied.
  • However, the derivative f(x)f'(x) involves x1/3x^{-1/3}, which is undefined at x=0x = 0. This means the function is not differentiable at x=0x = 0.

Thus, this does not contradict Rolle's Theorem, since the function is not differentiable on the entire interval (8,8)(-8, 8).

The correct conclusion is: This does not contradict Rolle’s Theorem, since f(0) does not exist, and so f is not differentiable on (8,8).\boxed{\text{This does not contradict Rolle's Theorem, since } f'(0) \text{ does not exist, and so } f \text{ is not differentiable on } (-8, 8).}


Do you need more details on any part of this explanation?

Here are some related questions you could explore:

  1. How is the cube root of a negative number defined in general?
  2. What are the key conditions of Rolle's Theorem?
  3. What happens if a function is not differentiable at a single point in the interval?
  4. Can a function still be continuous even if it's not differentiable everywhere?
  5. How do we find critical points where the derivative doesn't exist?

Tip: Always check if the function is differentiable across the entire interval when applying Rolle's Theorem!

Ask a new question for Free

By Image

Drop file here or Click Here to upload

Math Problem Analysis

Mathematical Concepts

Algebra
Differentiation
Rolle's Theorem

Formulas

f(x) = 4 − x^(2/3)
f'(x) = -2/3 * x^(-1/3)

Theorems

Rolle's Theorem

Suitable Grade Level

Grades 11-12 or Calculus 1