= , = , (It is what your got, and it is correct !) Next introduce new variable t = sin(x) for shortness. You will get = , = . Solve this quadratic by applying the quadratic fotmula = = . One root is = 1 ---> sin(x) = 1 ---> x = , k = 0, +/-1, +/-2, . . . The other root is = ---> sin(x) = ---> x = , k = 0, +/-1, +/-2, . . .