（sinx+cosx）/（sinx-cosx）=3求sin^2（x）+sinxcosx

sinx+cosx=3sinx-3cosx
2sinx=4cosx
tanx=2
cosx^2=1/（1+tanx^2）=1/5
sinx^2=1-cosx^2=4/5
sinxcosx=tanxcosx^2=2/5
sinx^2+sinxcosx=4/5+2/5=6/5