Решить: sin^2x +2sin( π -x)*cosx-3cos^2(2π -x)=0

sin^2 x + 2* sin x * cos x - 3 cos^2 x = 0;     /:cos^x ≠ 0;
sin^2 x / cos^2 x + 2 sin x *cos x / cos^2 x - 3 cos^2 x / cos^2 x = 0;
tg^2 x + 2 tg x - 3 = 0;
tg x = t;
t^2 + 2 t - 3 = 0;
D = 4 + 12 = 16 = 4^2;
 t1 = 1; ⇒ tg x = 1; ⇒ x = pi/4 + pi*k; k-X.
t2 = - 3; ⇒ tg x = -3; x = - arctg3 + pi*k ; k-Z