(a)

The trigonometric equation is .

Consider .

and 

and

Consider .

General solution of is , where is an integer.

The general solution is , where is an integer.

Consider .

General solution of is , where is an integer.

General solution is , where is an integer.

Thus, the solutions are and , where is an integer.

(b)

Find the angles in the interval .

The solutions are and , where is an integer.

Conisder . 

If , .

If , .

Consider .

If , .

If , .

If , .

Thus, the solutions are ,  and in the interval .

(a) The solutions are and , where is an integer.

(b) The solutions are ,  and in the interval .