Cos 2 π 6. 2cos2x. 2cos^2(x/2). Cos2x 1 cos2x 3sin2x. Sin 2 x/4 cos 2 x/4 sin π/2. Cos п/7 cos 2п/7 cos 4п/7. Cos пи/7 + cos 3пи/7 + cos 5пи/7. Cos п-7 /3 1/2. Cos 7pi/6. Cos^2(x-π)=1. Cos 3 π(x+2) = 2 1. Cos π(x+2)/3 = 1/2 решение. Cos〖(1/2〗 x+π/3)=-1/2. Cos(π/4-a) -cos(π/4+a)