是(z-1)/(z+1)
=(x+iy-1)/(x+iy+1)
=(x-1+iy)(x+1-iy)/[(x+1)^2+y^2]
=[x^2-1+y^2+2yi]/[(x+1)^2+y^2]
因此实部为(x^2+y^2-1)/[(x+1)^2+y^2]
虚部为2y/[(x+1)^2+y^2]