Math Problem Statement

Verify that the function satisfies the three hypotheses of Rolle's Theorem on the given interval. Then find all numbers c that satisfy the conclusion of Rolle's Theorem. (Enter your answers as a comma-separated list.) f(x) = sin(x/2) [𝜋/2, 3𝜋/2]

Solution

To verify the hypotheses of Rolle's Theorem and find the value(s) of cc, follow these steps:

Step 1: Verify the hypotheses of Rolle's Theorem

  1. The function f(x)=sin(x/2)f(x) = \sin(x/2) is continuous on [π/2,3π/2][ \pi/2, 3\pi/2 ].

    • sin(x/2)\sin(x/2) is a sine function, which is continuous everywhere. Hence, it is continuous on [π/2,3π/2][ \pi/2, 3\pi/2 ].
  2. The function f(x)=sin(x/2)f(x) = \sin(x/2) is differentiable on (π/2,3π/2)( \pi/2, 3\pi/2 ).

    • sin(x/2)\sin(x/2) is differentiable everywhere because it is a sine function, and its derivative f(x)=(1/2)cos(x/2)f'(x) = (1/2)\cos(x/2) exists for all xx.
  3. f(π/2)=f(3π/2)f(\pi/2) = f(3\pi/2): The function has equal values at the endpoints.

    • At x=π/2x = \pi/2: f(π/2)=sin((π/2)/2)=sin(π/4)=22.f(\pi/2) = \sin((\pi/2)/2) = \sin(\pi/4) = \frac{\sqrt{2}}{2}.
    • At x=3π/2x = 3\pi/2: f(3π/2)=sin((3π/2)/2)=sin(3π/4)=22.f(3\pi/2) = \sin((3\pi/2)/2) = \sin(3\pi/4) = \frac{\sqrt{2}}{2}.
    • Since f(π/2)=f(3π/2)f(\pi/2) = f(3\pi/2), the third hypothesis is satisfied.

Thus, all three hypotheses of Rolle's Theorem are satisfied.


Step 2: Apply Rolle's Theorem

Rolle's Theorem states that there exists at least one cc in (π/2,3π/2)(\pi/2, 3\pi/2) such that f(c)=0f'(c) = 0.

  1. Find f(x)f'(x): f(x)=sin(x/2),f(x)=12cos(x/2).f(x) = \sin(x/2), \quad f'(x) = \frac{1}{2} \cos(x/2).

  2. Set f(x)=0f'(x) = 0: 12cos(x/2)=0    cos(x/2)=0.\frac{1}{2} \cos(x/2) = 0 \implies \cos(x/2) = 0.

  3. Solve for xx: cos(x/2)=0    x/2=π2+kπ,kZ.\cos(x/2) = 0 \implies x/2 = \frac{\pi}{2} + k\pi, \quad k \in \mathbb{Z}. Multiply through by 2: x=π+2kπ,kZ.x = \pi + 2k\pi, \quad k \in \mathbb{Z}.

  4. Find xx in the interval (π/2,3π/2)(\pi/2, 3\pi/2):

    • For k=0k = 0, x=πx = \pi.
    • x=πx = \pi lies in (π/2,3π/2)(\pi/2, 3\pi/2).

Thus, the only value of cc is: c=π.c = \pi.


Final Answer:

The value of cc that satisfies the conclusion of Rolle's Theorem is: π.\boxed{\pi}.

Do you want detailed explanations of any of the steps or further elaboration?


Expanding Questions:

  1. How does differentiability affect the applicability of Rolle's Theorem?
  2. Can a discontinuous function satisfy Rolle's Theorem on a given interval? Why or why not?
  3. What is the geometric interpretation of Rolle's Theorem?
  4. What would happen if the endpoints of the function were not equal?
  5. Can you generalize Rolle’s Theorem to higher-dimensional functions?

Tip: When verifying Rolle's Theorem, always check each hypothesis carefully; even one failure invalidates the theorem!

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Math Problem Analysis

Mathematical Concepts

Calculus
Continuity
Differentiability
Critical Points

Formulas

Derivative of f(x) = sin(x/2) is f'(x) = (1/2)cos(x/2)
Rolle's Theorem: If f(a) = f(b) and f(x) is continuous on [a, b] and differentiable on (a, b), then there exists c in (a, b) such that f'(c) = 0

Theorems

Rolle's Theorem

Suitable Grade Level

Undergraduate Calculus (First Year)