Math Problem Statement

Does f(x) = |x| satisfy Roll’s conditions on [-1, 1] ? Justify your answer.

Solution

To determine whether f(x)=xf(x) = |x| satisfies Rolle's Theorem on the interval [1,1][-1, 1], we need to verify the following three conditions:

Rolle's Theorem Conditions:

  1. f(x)f(x) is continuous on the closed interval [a,b][a, b]:

    • The function f(x)=xf(x) = |x| is continuous for all real numbers, including on [1,1][-1, 1]. Therefore, this condition is satisfied.
  2. f(x)f(x) is differentiable on the open interval (a,b)(a, b):

    • The derivative of f(x)=xf(x) = |x| is: \begin{cases} 1 & \text{if } x > 0, \\ -1 & \text{if } x < 0. \end{cases}$$ However, $$f'(x)$$ is undefined at $$x = 0$$. Since $$x = 0$$ lies within the open interval $$(-1, 1)$$, $$f(x)$$ is not differentiable on the entire open interval. Thus, this condition is **not satisfied**.
  3. f(a)=f(b)f(a) = f(b):

    • At the endpoints of the interval [1,1][-1, 1], f(1)=1=1f(-1) = |{-1}| = 1 and f(1)=1=1f(1) = |1| = 1. Therefore, f(1)=f(1)f(-1) = f(1), and this condition is satisfied.

Conclusion:

Although f(x)=xf(x) = |x| satisfies the conditions of continuity on [1,1][-1, 1] and equal function values at the endpoints, it does not satisfy the differentiability condition on (1,1)(-1, 1). Therefore, Rolle's Theorem does not apply to f(x)=xf(x) = |x| on the interval [1,1][-1, 1].


Would you like to explore similar examples or delve deeper into this topic? Here are some related questions to consider:

  1. What happens if we modify the interval for f(x)=xf(x) = |x|?
  2. Can a function fail Rolle's Theorem due to endpoints instead of differentiability?
  3. How does differentiability impact the application of Rolle's Theorem?
  4. What is an example of a function that does satisfy Rolle's conditions on a specific interval?
  5. How does the absolute value function behave near sharp points or corners?

Tip: Rolle’s Theorem often hinges on differentiability, so check for sharp turns or cusps in the graph of a function!

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Math Problem Analysis

Mathematical Concepts

Calculus
Differentiability
Continuity

Formulas

Definition of derivative f'(x)

Theorems

Rolle's Theorem

Suitable Grade Level

Grades 11-12