You may have been thinking about the fact that the symbol $\displaystyle\sqrt{\ \text{ }\ }\usepackage{cmbright}\Huge\$ is defined to be the positive square root of a number. However, $\displaystyle-{1}\usepackage{cmbright}\Huge\$ has no square root at all. You cannot take a real number and multiply it by itself and end up with a negative number.