Solving an equation using the sum and difference formulas for cosine

The video tutorial explains the cosine sum and difference formulas, demonstrating how to apply them by substituting values and simplifying expressions. It emphasizes the importance of using parentheses to avoid errors and shows how to evaluate trigonometric functions using the unit circle. The tutorial concludes with solving trigonometric equations to find specific angle values within a given range.

Describe the process of rationalizing the denominator in the context of this problem.

What are the values of X when sine of X equals -√2/2?

What angles correspond to the sine of X being negative in the third and fourth quadrants?