(cosx-sinx+1)/(cosx+sinx+1)
令x=2t
=(cost^2-sint^2-2sintcost+sint^2+cost^2)/(cost^2-sint^2+2sintcost+sint^2+cost^2)
=2cost(1-sint)/2cost(1+sint)
=(1-sint)/(1+sint)
万能公式,得证