For the first one, rewrite the equation using the double-angle identity for sine, to get:

Now, divide through by then subtract from both sides, factor and use the zero-factor property to equate both factors to zero and solve.

For the second one, use a Pythagorean identity to get a quadratic in :

Now, distribute, and arrange in standard quadratic form, and you will find it factors nicely, and use the zero-factor property to equate both factors to zero and solve.