You switched the values of x and y. That is, when $\displaystyle{x}={3}\usepackage{cmbright}\Huge\$ , $\displaystyle{y}={0}\usepackage{cmbright}\Huge\$ . When $\displaystyle{x}={1}\usepackage{cmbright}\Huge\$ , $\displaystyle{y}={1}\usepackage{cmbright}\Huge\$ . When $\displaystyle{x}=-{1}\usepackage{cmbright}\Huge\$ , $\displaystyle{y}={2}\usepackage{cmbright}\Huge\$ .