为什么sin(2A+π/3)+sin(2A-π/3)=sin2ART
问题描述：
为什么sin(2A+π/3)+sin(2A-π/3)=sin2A
RT
答
sin(2A+π/3)+sin(2A-π/3)=sin2Acos（π/3)+cos2Asin(π/3)+sin2Acos（π/3)-cos2Asin(π/3)=2sin2Acos（π/3)=sin2A
答
你把等号左面的部分全展开算
答
左边=sin2Acosπ/3+cos2Asinπ/3+sin2Acosπ/3-cos2Asinπ/3
=2sin2Acosπ/3
=2sin2A*1/2
=sin2A=右边
命题得证