T=π
原式=sinx(1+tanx*（1-cosx）/sinx)=tanx为什么tan(x/2)=(1-cosx)/sinxtan(x/2)=(sinx/2)/cos(x/2)=2sin(x/2)cos(x/2)/2cos(x/2)^2=sin(x/2*2)/cos(x/2*2)+1=sinx/(cosx+1) 考虑到(1+cosx)(1-cosx)=sinx^2tan(x/2)=sinx/(cosx+1)=(1-cosx)/sinx