The trigonometric equation is .

Substitute the double angle formula .

Apply zero product property. \ \

and

and

Solve above two equations separately for solution.

First part

The general solution of is , where is any integer.

.

For , .

For , .

.

For , .

Therefore, the solutions in the interval are .

Second part

The general solution of is , where is any integer.

solution is

Substitute in , hence

Substitute in , hence \ \

Therefore,

Therefore,  the solutions in the interval are .

For complete solution we need to combine above two solutions

combine solutions is and

Arrange in ascending order

The solution for is .