已知角α的终边上一点P的坐标为(-√3,y),且sinα=（√3/4）y,求cosα及tanα的值

tanα=-y/√3
cosα=sinα/tanα=(√3/4)y/(-y/√3)=-3/4
(sinα)^2+(cosα)^2=1
sinα = √7/4,tanα = -√21/7,or,sinα = -√7/4,tanα = √21/7