三角函数证明题 sin(5/6π-a)+sin(5/6π+a)=cosa
问题描述:
三角函数证明题 sin(5/6π-a)+sin(5/6π+a)=cosa
答
sin(5/6π-a)+sin(5/6π+a)
=sin5π/6·cosa - cos5π/6·sina +sin5π/6·cosa + cos5π/6·sina
=sin5π/6·cosa + sin5π/6·cosa
=2sin5π/6·cosa
=2×(1/2)·cosa
=cosa