6sin^2 (p+x) + sin (p+x) cos (p-x) - cos^2x=0

Sin (pi + x) = - sin x

sin^2 (pi + x) = sin^2 x

cos (pi - x) = - cos x

Подставляем

6sin^2 x + (-sin x) (-cos x) - cos^2 x = 0

6sin^2 x + sin x*cos x - cos^2 x = 0

Делим все на cos^2 x

6tg^2 x + tg x - 1 = 0

(2tg x + 1) (3tg x - 1) = 0

tg x = - 1/2; x1 = - arctg (1/2) + pi*k

tg x = 1/3; x2 = arctg (1/3) + pi*n