cos a/2=0.8 найти sina 0°

 cos(a/2) ^{2} +sin(a/2) ^{2} =1  -> sin(a/2) ^{2} = sqrt{1-cos(a/2) ^{2} } = sqrt{0,36}  = 0,6sin(a) = 2*sin(a/2)*cos(a/2)  =  2* 0,6*0,8 = 0,96