David Legrand

<math>\begin{matrix}z_3 &=& \begin{matrix}z_1 \times z_2 &=& \rho_1\times\exp(i(\theta_1 + 2k_1\pi)) \times \rho_2\times\exp((i\theta_2 + 2k_2\pi)) \\ \ &=& \rho_1\times\rho_2 \times \exp(i(\theta_1 + 2k_1\pi + \theta_2 + 2k_2\pi)) \\ \ &=& \rho_1\times\rho_2 \times \exp(i(\theta_1 + \theta_2 + 2(k_1 + k_2)\pi))\end{casesmatrix} \\ \ &=& \rho_3 \times \exp(i(\theta_3 + 2k_3\pi))\end{casesmatrix}</math>