sin[(α+β)-α]=msin[(α+β)+α]
sin(α+β)cosα-cos(α+β)sinα=msin(α+β)cosα+mcos(α+β)sinα
(1-m)sin(α+β)cosα=(1+m)cos(α+β)sinα
tan(α+β)=[(1+m)/(1-m)]tanα
所以(1+m)/(1-m)=3
m=0.5