tanα/(tanα-1)=-1,则tanα=-tanα+1、tanα=1/2.
1)(sina-3cosa)/(sina+cosa) 分子分母同除cosa
=(tana-3)/(tana+1)
=(1/2-3)/(1/2+1)
=-5/3
2)(sina)^2+sinacosa+2
=[(sina)^2+sinacosa+2(sina)^2+2(cosa)^2]/[(sina)^2+(cosa)^2]
=[3(sina)^2+sinacosa+2(cosa)^2]/[(sina)^2+(cosa)^2] 分子分母同除(cosa)^2
=[3(tana)^2+tana+2]/[(tana)^2+1]
=(3/4+1/2+2)/(1/4+1)
=13/5