It appears that you multiplied the real parts and the imaginary parts and added them together, thinking that $\displaystyle-{{i}}^{{2}}=-{1}\usepackage{cmbright}\Huge\$ . However $\displaystyle{{i}}^{{2}}=-{1}\usepackage{cmbright}\Huge\$ , so $\displaystyle-{{i}}^{{2}}={1}\usepackage{cmbright}\Huge\$ .