       Arguments of products and quotients
            </h2>

            <p>
                If  $z_1= r_1e^{i\theta_1}$ and $z_2= r_2e^{i\theta_2},$ then
                \begin{eqnarray}\label{product}
                z_1z_2 = \left(r_1r_2\right)e^{i\left(\theta_1 + \theta_2\right)}
                \end{eqnarray}
                implies 
                \begin{eqnarray}\label{arg-product}
                \arg\left(z_1z_2\right) = \arg\left(z_1\right) + \arg\left(z_2\right).
                \end{eqnarray}
