已知cot(a+拍/3)=-3则tan(2a-拍/3)=?
问题描述：
已知cot(a+拍/3)=-3则tan(2a-拍/3)=?
答
cot(a+π/3)=-3=tan[π/2-(a+π/3)]=tan(π/6-a)=-tan(a-π/6)
tan(a-π/6)=3
tan(2a-π/3)=2tan(a-π/6)/[1-tan^2(a-π/6)]=6/(-8)=-3/4