решить уравнение( 0,5cosПt)^2=0,125
0.25 cos^2 (pit)=0.125
cos^2(pit) =0.25
cos(pit) =0.5 cos(pit) =-0.5
pit = +-pi/3 +2pin pit = -+2pi/3+2pin
t = +-1/3 =2n t = +-2/3 +2n