A function $u=f(x,y)$ with continuous second partial derivatives satisfying Laplace's equation $\frac{de{l}^{2}u}{del{x}^2}+\frac{de{l}^{2}u}{del{y}^2}=0is$ called $a$

harmonic function.

Calculate the indicated derivatives and determine $if$ the function $u(x,y)=x^{3}y-x{y}^{3}is$ harmonic.

$\frac{de{l}^{2}u}{del{x}^2}=$

$\frac{de{l}^{2}u}{del{y}^2}=$

$Is$ the function $u=x^{3}y-x{y}^3$ harmonic?

$no$

yes