由题知,设tanα/(tanα-1)=-1所以,tanα=1/2tan2α=(2tanα)/(1-tan²α)=1/(3/4)=4/3所以,sin2α=4/5,cos2α=3/5或sin2α=-4/5,cos2α=-3/5所以,7/(sin2α+sinαcosα+cos2α)=7/(1.5*sin2α+cos2α)=±35/9...