Evaluate the double angle of cosine from a triangle

The video tutorial explains how to evaluate the cosine of two Theta given a trigonometric equation with constraints. It covers the importance of understanding the quadrant in which the angle lies and addresses common mistakes in drawing triangles. The tutorial then guides through the process of using the cosine formula to find the solution, emphasizing the correct application of trigonometric identities and the Pythagorean theorem.

Explain why the values of sine and cosine are negative in the third quadrant.

What is the value of cosine squared of Theta minus sine squared of Theta based on the triangle?