You may have switched the x-value and y-value when substituting them into the equation. Substituting $\displaystyle{\left(-{2},{3}\right)}\usepackage{cmbright}\Huge\$ into $\displaystyle{2}{y}-{5}{x}<{3}\usepackage{cmbright}\Huge\$ gives you $\displaystyle{6}+{10}<{3}\usepackage{cmbright}\Huge\$ , which is a false statement. So $\displaystyle{\left(-{2},{3}\right)}\usepackage{cmbright}\Huge\$ is not a solution to the inequality.