上式可化简为
s*(v1+v2)/2v1*v2-2s/(v1+v2)
=s*(v1+v2)*(v1+v2)/(2v1*v2*(v1+v2))-4sv1*v2/(2v1*v2*(v1+v2))
=(v1-v2)*(v1-v2)*s/(2v1*v2*(v1+v2))
v1/=v2
得证