Evaluate using the half angle formula for cosine

The video tutorial explains the cosine half angle formula and its application. It begins by introducing the formula and determining the quadrant for u/2, which affects the sign of the cosine value. The instructor then solves for u, calculates the cosine of pi over 4 using the unit circle, and simplifies the resulting fractions. The tutorial emphasizes understanding the trigonometric concepts and applying them to solve problems.

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