sinαcosβ+cosαsinβ+2sinαsinβ
tanatanb=-2
tana+tanb=-(-4)/1=4
sinasinb/cosacosb=-2
sinasinb=-2cosacosb.1
sina/cosa+sinb/cosb=(sinacosb+sinbcosa)/(cosacosb)=4
sinacosb+sinbcosa=4cosacosb.2
1,2代入：sinαcosβ+cosαsinβ+2sinαsinβ得：
4cosacosb+2*(-2cosacosb)=0