没分直说,别那么横 f(x)={[（sinx)^2+(cosx)^2]^2-(sinxcosx)^2}/[2(1-sinxcosx)] =[1-(sinxcosx)^2]/[2(1-sinxcosx)] =(1+sinxcosx)(1-sinxcosx)/[2(1-sinxcosx)] =(1+sinxcosx)/2 =(sin2x)/4+1/2