When simplifying, you may have forgotten that a negative times a negative is positive, or that a negative times a positive is negative.

$\displaystyle{4}{\left(-{5}\right)}={8}-{6}{\left(-{2}\right)}\usepackage{cmbright}\Huge\$ or $\displaystyle-{20}={8}+{12}\usepackage{cmbright}\Huge\$ or $\displaystyle-{20}={20}\usepackage{cmbright}\Huge\$

This is not a true statement, so the ordered pair $\displaystyle{\left(-{2},-{5}\right)}\usepackage{cmbright}\Huge\$ is not a solution to the equation.