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Ch. 7 - Transcendental Functions
Hass - Thomas' Calculus 15th Edition
Hass15th EditionThomas' CalculusISBN: 9780137616077Not the one you use?Change textbook
All textbooksHass 15th EditionCh. 7 - Transcendental FunctionsProblem 7.3.130
Chapter 7, Problem 7.3.130

130. Where does the periodic function f(x) = 2e^(sin(x/2)) take on its extreme values, and what are these values?
Graph of the periodic function y = 2e^(sin(x/2)) showing smooth oscillations with labeled x and y axes.

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1
Identify the function given: \(f(x) = 2e^{\sin(\frac{x}{2})}\), which is periodic due to the sine function inside the exponent.
To find the extreme values, compute the derivative \(f'(x)\) using the chain rule: \(f'(x) = 2e^{\sin(\frac{x}{2})} \cdot \cos(\frac{x}{2}) \cdot \frac{1}{2}\).
Set the derivative equal to zero to find critical points: \(f'(x) = 0 \Rightarrow 2e^{\sin(\frac{x}{2})} \cdot \cos(\frac{x}{2}) \cdot \frac{1}{2} = 0\). Since \(2e^{\sin(\frac{x}{2})} \neq 0\), this simplifies to \(\cos(\frac{x}{2}) = 0\).
Solve \(\cos(\frac{x}{2}) = 0\) for \(x\): \(\frac{x}{2} = \frac{\pi}{2} + k\pi\), where \(k\) is any integer, so \(x = \pi + 2k\pi\).
Evaluate \(f(x)\) at these critical points to find the extreme values: \(f(x) = 2e^{\sin(\frac{x}{2})}\), and since \(\sin(\frac{x}{2})\) oscillates between -1 and 1, the minimum and maximum values correspond to \(\sin(\frac{x}{2}) = -1\) and \(\sin(\frac{x}{2}) = 1\), respectively.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Periodic Functions

A periodic function repeats its values at regular intervals called periods. Understanding the period helps identify where the function's behavior repeats, which is essential for locating extreme values within one period and extending that knowledge to all periods.
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Extreme Values of a Function

Extreme values are points where a function reaches local maxima or minima. These occur where the derivative is zero or undefined, and the function changes direction. Finding these points involves differentiating the function and solving for critical points.
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Average Value of a Function

Chain Rule and Differentiation of Composite Functions

The function f(x) = 2e^(sin(x/2)) is a composite function involving an exponential and a trigonometric function. Differentiating it requires applying the chain rule, which handles the derivative of a function inside another function, crucial for finding critical points.
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The Chain Rule for 3+ Functions
Related Practice
Textbook Question

Solve the initial value problems in Exercises 55–58.


57. d²y/dx² = 2e^(−x),y(0) = 1,y′(0) = 0

Textbook Question

Verify the integration formulas in Exercises 111–114.

113. ∫ (arcsin x)² dx = x(arcsin x)² - 2x + 2 √(1 - x²) arcsin x + C

Textbook Question

Rewrite the expressions in Exercises 5–10 in terms of exponentials and simplify the results as much as you can.

9. (sinh(x)+cosh(x))⁴

Textbook Question

90. Find f'(0) for 

f(x) = e^(-1/x²), x≠0

   = 0, x = 0.

1
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Textbook Question

In Exercises 21–48, find the derivative of y with respect to the appropriate variable.

47. y=(arccot(x³))³

Textbook Question

In Exercises 7–26, find the derivative of y with respect to x, t, or θ, as appropriate.

y = e^(θ)(sinθ + cosθ)