Math Problem Statement

find the value of c that satisfies rolles theorem on [0,2pi] for the function sin2x

Solution

To find the value(s) of cc that satisfy Rolle's Theorem for f(x)=sin(2x)f(x) = \sin(2x) on the interval [0,2π][0, 2\pi], we proceed as follows:

Steps:

  1. Check the conditions of Rolle's Theorem:

    • The function f(x)f(x) is continuous on [0,2π][0, 2\pi] and differentiable on (0,2π](0, 2\pi].
    • f(0)=sin(20)=0f(0) = \sin(2 \cdot 0) = 0 and f(2π)=sin(22π)=0f(2\pi) = \sin(2 \cdot 2\pi) = 0, so f(0)=f(2π)f(0) = f(2\pi).

    Since f(x)f(x) satisfies all conditions of Rolle's Theorem, there exists at least one c(0,2π)c \in (0, 2\pi) such that f(c)=0f'(c) = 0.

  2. Find the derivative f(x)f'(x): f(x)=ddxsin(2x)=2cos(2x).f'(x) = \frac{d}{dx} \sin(2x) = 2\cos(2x).

  3. Set f(c)=0f'(c) = 0 and solve: 2cos(2c)=0cos(2c)=0.2\cos(2c) = 0 \quad \Rightarrow \quad \cos(2c) = 0.

    The cosine function is zero at 2c=π2,3π2,5π2,2c = \frac{\pi}{2}, \frac{3\pi}{2}, \frac{5\pi}{2}, \dots, which simplifies to: 2c=π2+nπ,nZ.2c = \frac{\pi}{2} + n\pi, \quad n \in \mathbb{Z}.

    Dividing by 2: c=π4+nπ2,nZ.c = \frac{\pi}{4} + \frac{n\pi}{2}, \quad n \in \mathbb{Z}.

  4. Find cc within the interval (0,2π)(0, 2\pi): Substitute n=0,1,2,3,n = 0, 1, 2, 3, \dots and keep cc in (0,2π)(0, 2\pi):

    • n=0n = 0: c=π4c = \frac{\pi}{4}.
    • n=1n = 1: c=π4+π2=3π4c = \frac{\pi}{4} + \frac{\pi}{2} = \frac{3\pi}{4}.
    • n=2n = 2: c=π4+π=5π4c = \frac{\pi}{4} + \pi = \frac{5\pi}{4}.
    • n=3n = 3: c=π4+3π2=7π4c = \frac{\pi}{4} + \frac{3\pi}{2} = \frac{7\pi}{4}.
    • n=4n = 4: c=π4+2π=9π4c = \frac{\pi}{4} + 2\pi = \frac{9\pi}{4}, which is outside (0,2π)(0, 2\pi).

Thus, the values of cc are: c=π4,3π4,5π4,7π4.c = \frac{\pi}{4}, \frac{3\pi}{4}, \frac{5\pi}{4}, \frac{7\pi}{4}.

Final Answer:

The values of cc that satisfy Rolle's Theorem are: c=π4,3π4,5π4,7π4.c = \frac{\pi}{4}, \frac{3\pi}{4}, \frac{5\pi}{4}, \frac{7\pi}{4}.


Do you want me to elaborate on Rolle's Theorem or explain any specific step in more detail?

Related Questions:

  1. How does differentiability ensure the existence of a critical point in Rolle's Theorem?
  2. What is the geometrical interpretation of Rolle's Theorem for sin(2x)\sin(2x)?
  3. What happens if f(a)f(b)f(a) \neq f(b) in Rolle’s Theorem?
  4. How does cos(2x)=0\cos(2x) = 0 relate to the critical points of sin(2x)\sin(2x)?
  5. Can Rolle's Theorem be applied to non-polynomial functions, and why?

Tip:

To apply Rolle's Theorem, always verify the conditions (continuity, differentiability, and equal endpoints) before solving.

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Math Problem Analysis

Mathematical Concepts

Calculus
Rolle's Theorem
Trigonometric Functions

Formulas

f'(x) = d/dx [sin(2x)] = 2cos(2x)

Theorems

Rolle's Theorem

Suitable Grade Level

Grades 11-12