The trigonometric function is and  .

If , then .

.

From Pythagorean theorem,

Since and .

Therefore, lies in fourth quadrant.

lies in fourth quadrant, is negative and is positive.

.

.

(a) Find .

Use Double-angle formula: .

.

Substitute and .

.

(b) Find .

Use Double-angle formula: .

.

Substitute and .

.

(c) Find .

Use Half-angle formula: .

.

Substitute .

since lies in fourth quadrant,  .

, lies in second quadrant.

Therefore, is positive.

.

(d) Find .

Use Half-angle formula: .

Substitute .

Here lies in second quadrant, therefore is negative.

.

(a) .

(b) .

(c) .

(d) .