u=ln[根号（x^2+y^2）]
=1/2ln(x^2+y^2)
z'x=ve^(uv)*1/[2(x^2+y^2)]*2x+ue^(uv)*1/(1+y^2/x^2)*(-y/x^2)
=ve^(uv)*x/(x^2+y^2)-ue^(uv)*y/(x^2+y^2) (u,v自己代入)
z'y=ve^(uv)*1/[2(x^2+y^2)]*2y+ue^(uv)*1/(1+y^2/x^2)*(1/x)
=ve^(uv)*y/(x^2+y^2)+ue^(uv)*x/(x^2+y^2) (u,v自己代入)