cos^2π/12-sin^2π/12等于

cos^2π/12-sin^2π/12等于
cos^2π/12-sin^2π/12等于

cos^2π/12-sin^2π/12等于
cos²π/12-sin²π/12
=cos(2×π/12)
=cos(π/6)
=√3/2
cos2α=cos²a-sin²a

你好！
sinπ/12??cosπ/12=sin??π/12-cos??π/12-sinπ/12*cosπ/12=-cosπ/6-(sinπ/6)/2=-√3/2-1/4.