Sin^2(π/8)-Cos^2(π/8)
问题描述：
Sin^2(π/8)-Cos^2(π/8)
答
=-[cos²π/8-sin²π/8)
=-cosπ/4
=-√2/2
Sin^2(π/8)-Cos^2(π/8)
=-[cos²π/8-sin²π/8)
=-cosπ/4
=-√2/2