2sin²x-sinx-1=0 или 1+cos2X=0 sinx=t cos2x=-1 2t²-t-1=0 2x=п+2пn t=-1/2 x=п/2+пn t=1 sinx=1 x=п/2+2пn sinx=-1/2 x=((-1)^k+1)п/6+пk