化简求sin^2(a-π/3)+sin^2(a+π/3)+sin^2a
问题描述：
化简求sin^2(a-π/3)+sin^2(a+π/3)+sin^2a
答
sin^2(a-π/3)+sin^2(a+π/3)+sin^2a
=1/2-cos(2a-2π/3)/2+1/2-cos(2a+2π/3)/2+1/2-cos2a/2
=3/2