$\displaystyle{\left({2}{x}-{9}\right)}{\left({2}{x}-{9}\right)}\usepackage{cmbright}\Huge\$ is the factorization of a perfect square trinomial. Our polynomial is the difference of two squares, so a correct factorization looks like $\displaystyle{\left({r}+{s}\right)}{\left({r}-{s}\right)}\usepackage{cmbright}\Huge\$ .