Substitute $\displaystyle{x}={3}\usepackage{cmbright}\Huge\$ and $\displaystyle{y}=-{2}\usepackage{cmbright}\Huge\$ into the equation: $\displaystyle{2}{\left({3}\right)}-{7}{\left(-{2}\right)}={20}\usepackage{cmbright}\Huge\$

Simplify: $\displaystyle{6}+{14}={20}\usepackage{cmbright}\Huge\$ or $\displaystyle{20}={20}\usepackage{cmbright}\Huge\$

The statement is true, so $\displaystyle{\left({3},-{2}\right)}\usepackage{cmbright}\Huge\$ is a solution to the equation.