Consider $x^{2}-xy-20y^{2}$ as a polynomial over variable $x$.
$$x^{2}-yx-20y^{2}$$
Find one factor of the form $x^{k}+m$, where $x^{k}$ divides the monomial with the highest power $x^{2}$ and $m$ divides the constant factor $-20y^{2}$. One such factor is $x-5y$. Factor the polynomial by dividing it by this factor.
