sin^4π/8-cos^4π/8=?
问题描述：
sin^4π/8-cos^4π/8=?
答
sin^4π/8-cos^4π/8=
=(sin^2π/8-cos^2π/8)(sin^2π/8+cos^2π/8)
=sin^2π/8-cos^2π/8
=-cosπ/4
=-√2/2