sinx+sin2x=cosx+2cos²x

sinx + 2sinx*cosx - cosx - 2cosx*cosx = 0

sinx(1+2cosx) - cosx(1+2cosx) = 0

(1+2cosx)(sinx - cosx) = 0

1) cosx= -1/2;        x=±2п/3 +2пk, kC Z    

2) sinx = cosx   (делим на cosx≠0)      tgx=0;   x=пk, kC Z