tanx/(tanx-1)=-1 故tanx=1/2
(sinx-3cosx)/(sinx+cosx)=(tanx-3)/(tanx+1)=(-5/2)/(3/2)=-5/3sin^2x+sinxcosx+2=要过程 越细致越好，谢谢sin^2x+sinxcosx+2=(sin^2x+sinxcosx)/(sin^2x+cos^2x)+2=(上下同除cos^2x)=(tan^2x+tanx)/(tan^2x+1)+2=(1/4+1/2)/(1/4+1)+2=13/5