If u=x^2tan-1y/x-y^2tan-1x/y show that ∂^2u/∂x∂y=(x^2-y^2)/((x^2+y^2)

If u=x^2tan-1y/x-y^2tan-1x/y show that ∂^2u/∂x∂y=(x^2-y^2)/((x^2+y^2)

If u=x^2tan-1y/x-y^2tan-1x/y show that ∂^2u/∂x∂y=(x^2-y^2)/((x^2+y^2)