Math Problem Statement

The derivative of the function f is defined by f′(x)=(*x^*2+2)cos(x+5). What is the x-coordinate of the absolute maximum value of the function f on the closed interval [−4,2]? You may use a calculator and round your answer to the nearest thousandth.

Solution

To find the absolute maximum value of the function f(x)f(x) on the closed interval [4,2][-4, 2], we will apply the First Derivative Test and evaluate the function at critical points and at the endpoints.

Steps to solve:

  1. Find the critical points: The critical points occur when f(x)=0f'(x) = 0. We're given f(x)=(x2+2)cos(x+5)f'(x) = (x^2 + 2)\cos(x + 5). To find critical points, set f(x)=0f'(x) = 0: (x2+2)cos(x+5)=0(x^2 + 2)\cos(x + 5) = 0 Since x2+20x^2 + 2 \neq 0 for any real xx (because x2+22x^2 + 2 \geq 2), the only way this product equals 0 is when: cos(x+5)=0\cos(x + 5) = 0

  2. Solve cos(x+5)=0\cos(x + 5) = 0: The cosine function is zero at π2+nπ\frac{\pi}{2} + n\pi, for integer nn. Therefore: x+5=π2+nπx + 5 = \frac{\pi}{2} + n\pi Solving for xx: x=π25+nπx = \frac{\pi}{2} - 5 + n\pi This gives us a general solution for xx, but we are only interested in solutions within the interval [4,2][-4, 2].

  3. Find specific solutions: By substituting different integer values of nn and solving for xx, we get the possible critical points within the interval [4,2][-4, 2]:

    • For n=0n = 0, x=π253.429x = \frac{\pi}{2} - 5 \approx -3.429
    • For n=1n = 1, x=3π250.288x = \frac{3\pi}{2} - 5 \approx -0.288

    So the critical points are x3.429x \approx -3.429 and x0.288x \approx -0.288.

  4. Evaluate the function at the critical points and endpoints: Since we do not have an explicit formula for f(x)f(x), we can only evaluate the function f(x)f(x) at the critical points and endpoints using the information from f(x)f'(x).

    The endpoints are x=4x = -4 and x=2x = 2.

  5. Determine the absolute maximum: Using the calculator, evaluate the function at the critical points and the endpoints (by analyzing the sign changes of f(x)f'(x) around those points) to find the xx-coordinate where f(x)f(x) has an absolute maximum.

    After evaluating, the absolute maximum occurs at x3.429x \approx -3.429.

Conclusion:

The xx-coordinate of the absolute maximum value of the function f(x)f(x) on the closed interval [4,2][-4, 2] is approximately 3.429\boxed{-3.429}.


Would you like further details or clarifications on any of these steps?

Here are some related questions:

  1. How do we find critical points for a general function?
  2. What is the First Derivative Test, and how does it work?
  3. How can we evaluate trigonometric equations like cos(x)=0\cos(x) = 0 in different intervals?
  4. What is the significance of closed intervals in optimization problems?
  5. How does the behavior of the derivative inform us about maximum and minimum points?

Tip: Always check both critical points and endpoints when looking for absolute extrema on a closed interval.

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Math Problem Analysis

Mathematical Concepts

Calculus
Critical Points
Maxima and Minima
Trigonometric Functions

Formulas

f'(x) = (x^2 + 2)cos(x + 5)
cos(x) = 0

Theorems

First Derivative Test
Critical Point Theorem

Suitable Grade Level

College Calculus