When you substitute $\displaystyle-{1}\usepackage{cmbright}\Huge\$ for x you get $\displaystyle{3}{{x}}^{{2}}={3}{{\left(-{1}\right)}}^{{2}}\usepackage{cmbright}\Huge\$ . You need to use the correct order of operations. Apply the exponent first, and then multiply. Also, if you square a negative number you will get a positive number.