你的结论有误
∵ tan(x/2)
=sin(x/2)/cos(x/2)
=2sin²(x/2)/[2sin(x/2)cos(x/2)]
=(1-cosx)/sinx
≠cosx/(1-sinx)
但是 (pai-2)/2
=pai/2-1
=1/(pai/2-1)
∴ 结论不对.