The trigonometric equation is in the interval .

.

From Pythagorean theorem,

The square of the hypotenuse is equal to sum the squares of the other two sides.

.

Where lies in first quadrant.

In first quadrant, the six trigonometric functions are positive.

.

(a)

Find .

Use Double-angle formula: .

Substitute and .

.

(b)

Find .

Use Double-angle formula: .

Substitute and .

.

(c)

Find .

Use Half-angle formula: .

Substitute .

Where lies in first quadrant, since lies in first quadrant.

.

(d)

Find .

Use Half-angle formula: .

Substitute .

Where lies in first quadrant, since lies in first quadrant.

.

(a) .

(b) .

(c) .

(d) .