The trigonometric equation is .

Double angle formula: .

Apply zero product property.

and .

Consider first part .

The general solution of is , where is any integer.

For , 

For , .

For , .

For , 

For , 

Therefore, the solutions in the interval are .

Consider second part

The general solution of is , where is any integer.

solution is

Substitute in , hence .

Substitute in , hence .

Substitute in , hence .

Hence, .

Therefore, .

Therefore,  the solutions in the interval are .

.

For complete solution we need to combine above two solutions

combine solutions is

Arrange in ascending order

The solution for is .