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Single Variable Calculus

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Moderate

Integral of Cosine to the Fourth

SVCALC-AZF0XQ

Evaluate the integral:

$$\int_{\pi/4}^{3\pi/4}\cos^4 2x dx$$

A

$0$

B

$\dfrac{3\pi}{16}$

C

$\dfrac{3\pi}{8}$

D

$\dfrac{2\pi}{3}+\dfrac{1}{2}$