(cos15度-cos75度)(sin75度+sin15度)等于多少
问题描述：
(cos15度-cos75度)(sin75度+sin15度)等于多少
答
=(sin75-cos75)(sin75+cos75)
=sin²75-cos²75
=-(cos²75-sin²75)
=-cos(2×75)
=-cos150
=√3/2