# Chapter 4 - Section 4.2 - Trigonometric Functions: The Unit Circle - Exercise Set - Page 548: 39

$\frac{\sqrt 2}{2}$

#### Work Step by Step

cos($\frac{\pi}{4}$ + 2$\pi$) = cos$\frac{\pi}{4}$ and cos$\frac{\pi}{4}$ = $\frac{\sqrt 2}{2}$.

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