text: Those are just disguised factoring problems.\n\nConsider:\n\ncos^3x = cos x\n\ncos^3 x - cos x = 0\n\ncos x(cos^2 x - 1) = 0\n\n-cos x(sin^2 x) = 0\n\nSo cos x = 0 or sin^2 x = 0\n\nand solve from there.\n\nFor the other, note that the equation is quadratic in sin x.  Try the substitution y = sin x:\n\n2y^2 + y + 1 = 0\n\nSolve that for y and resubstitute sin x.