Hello, supersaiyan!

(a) We're told that: .1) If

evaluate: .

We have a right triangle with angle and:

Using Pythagorus, we find that: .

Since is in Quadrant 1, is in Quadrant 1.

. . Hence: .

Double-angle Identity: .

Hence: .

(b) Half-angle Identity: .

We are given: .2. If

evaluate: .

Since is in Quadrant 2: . . . . Then: .

Hence: .