решите уравнение 2 sin²x+cos x–1=0

2(1-cos^2x) + cos x - 1 =0; 2 - 2 cos^2 x  +cos x -1 =0;- 2 cos^2 x + cos x +1 =0; 2 cos^2 x - cos x - 1 =0;cos x =t;  -1 ≤ t≤ 1;2t^2 -t - 1=0; D=1+8=93^2; t1= 1;⇒ cos x =1; ⇒x = 2pik; k∈Z;t2= -1/2; ⇒cos x = -1/2; ⇒ x = + - pi/3 + 2pin; n∈Z