It appears that you multiplied the real parts and the imaginary parts and added them together, realizing that $\displaystyle{{i}}^{{2}}=-{1}\usepackage{cmbright}\Huge\$ . A binomial multiplied by a binomial will have four terms when you use the distributive property correctly. In the case of a binomial times a binomial, we sometimes use the mnemonic FOIL to remember how to get the four terms.