How to evaluate for cos without using a calculator or the unit circle

The video tutorial explains how to evaluate trigonometric functions using reference angles. It covers the concept of coterminal angles, how to determine the quadrant of an angle, and the significance of reference angles in trigonometry. The tutorial emphasizes the importance of understanding the quadrant to determine the sign of trigonometric values and provides a practical example using the cosine function.

What new insight or understanding did you gain from this video?