You evaluated $\displaystyle\frac{{{y}_{{1}}-{x}_{{1}}}}{{{y}_{{2}}-{x}_{{2}}}}\usepackage{cmbright}\Huge\$ , but the slope formula is: $\displaystyle{m}=\frac{{{y}_{{2}}-{y}_{{1}}}}{{{x}_{{2}}-{x}_{{1}}}}\usepackage{cmbright}\Huge\$