=(1-sinx+cosx)/(1-cosx-sinx)+(1-cosx-sinx)/(1+cosx-sinx)
=[(1+cosx-sinx)(1+cosx+sinx)]/[(1-cosx-sinx)(1+cosx+sinx)]+[(1-cosx-sinx)(1-cosx+sinx)]/[(1+cosx-sinx)(1-cosx+sinx)]
=(1+2cosx+cos2x)/(-sin2x)+(1-2cosx+cos2x)/(sin2x)
=(-4cosx)/sin2x
= -2/sinx
1-cos2x/2 + +√3（sin2x）/2
=sin(2x-π/6)+1/2
x∈【π/4,π/2】
2x∈【π/2,π】
2x-π/6∈【π/3,5π/6】
f(x)max=√3/2 +1/2