You may have simplified $\displaystyle{{\left({5}-{9}\right)}}^{{2}}\usepackage{cmbright}\Huge\$ incorrectly and gotten $\displaystyle-{16}\usepackage{cmbright}\Huge\$ instead of 16. Operations inside parentheses come before exponents. So if you have $\displaystyle{{\left(-{4}\right)}}^{{2}}\usepackage{cmbright}\Huge\$ , you are squaring a negative number and will get a positive result.