2sinx-3cosx=02sinx=3cosxtanx=3/22(sinx)^2+sinxcosx-(cos)^2=(2sinx-cosx)(sinx+cosx)=(3cosx-cosx)(3cosx/2+cosx)=5(cosx)^2=5*[(cos2x+1)/2]因为cos2x=[1-(tanx)^2]/[1+(tanx)^2]=(1-9/4)/(1+9/4)=-5/13所以原式...