You may have ignored the absolute value symbols and thought that $\displaystyle{\left|{2}-{8}\right|}\usepackage{cmbright}\Huge\$ is equal to $\displaystyle-{6}\usepackage{cmbright}\Huge\$ . Remember that the absolute value of a negative number is a positive number, so $\displaystyle{\left|{2}-{8}\right|}={6}\usepackage{cmbright}\Huge\$ .