tana=-1/2,tan(a-b)=-2/5,则tanb=?
问题描述：
tana=-1/2,tan(a-b)=-2/5,则tanb=?
答
tanb=tan[(a-b)-a]
=[tan(a-b)-tana]/[1+tan(a-b)tana]
=[(-2/5)-(1/2)]/[1+(2/5)*(1/2)]
=(-9/10)/(12/10)
=-9/12
=-3/4