Evaluate inverse trig functions without a calculator

The video tutorial explains how to find the cosine inverse of an angle, focusing on the restrictions of inverse functions. It discusses the unit circle, identifying angles in different quadrants, and the importance of function uniqueness. The tutorial emphasizes that a function must have a unique output for each input, using the vertical line test as a reference. It concludes with a calculator check to verify the angle in degrees.

What is the restriction on the cosine function when finding the inverse?

Why can't a function have two different outputs for the same input?