Evaluating trigonometric functions is all about knowing the unit circle (It is strongly recommended to memorize the trivial angles).
Let’s see how it works, here’s an example using a simple manipulation (click here):
Here’s an example using the periodic property (click here):
Here’s an example using trigonometric identity (click here):
Evaluating trigonometric equations might be somewhat tricky at first, but with practice you will use the same techniques over and over again…