How to evaluate the half angle of cosine given an angle

The video tutorial covers the calculation of cosine values in different quadrants, focusing on the second quadrant where cosine is negative. It explains how to derive Theta from given values and discusses the unit circle's role in understanding cosine values. The tutorial also demonstrates simplifying trigonometric expressions and concludes with a brief introduction to the next topic.

What is the cosine of five π/4?

How can you rewrite the expression involving the square root of 2 divided by 4?