tanx=2,tan(x-y)=-3/5,则tany=?
问题描述：
tanx=2,tan(x-y)=-3/5,则tany=?
答
tan(x-y)=(tanx-tany)/(1+tanxtany)
(2-tany)/(1+2tany)=-3/5
3+6tany=5tany-10
tany=-13