若tan(3x+y)=2,tan(x+y)=-4 求tan2x

问题描述:

若tan(3x+y)=2,tan(x+y)=-4 求tan2x


tan2x
=tan[(3x+y)-(x+y)]
=[tan(3x+y)-tan(x+y)]/[1+tan(3x+y)tan(x+y)]
=6/(1-8)
=-6/7