证明sinA+sin(A+2π/3)+sin(A-2π/3)=0
问题描述：
证明sinA+sin(A+2π/3)+sin(A-2π/3)=0
答
sinA+sin(A+2π/3)+sin(A-2π/3)
=sinA+sinAcos2π/3+cosAsin2π/3+sinAcos2π/3-cosAsin2π/3
=sinA+2sinAcos2π/3
=sinA+2sinA*(-1/2)
=sinA-sinA
=0.