Question

cos^2a-4sin^2(a/2)*cos^2(a/2)
a - альфа

Answer 1

cos²a-4sin²(a/2)*cos²(a/2)=cos²a-2(2sin²(a/2)*cos²(a/2))=cos²a-2sin²a=1-sin²a-2sin²a=1-3sin²a.