Помогите вычислить cos^2 150°- (sin 70°cos 40°-cos 70° cos50°) ^2

cos^2 150- (sin 70 cos 40-cos70 cos (90-40) ^2cos^2 150- (sin 70 cos 40-cos 70 sin 40) ^2cos^2 150- (sin 30) ^2=cos^2 (180-30) — (sin 30) ^2=cos^2 30-sin^2 30=3/4-1/4=2/4=1/2