\documentclass[12pt]{article}

\begin{document}
\pagestyle{empty}
\begin{eqnarray*}
E(\phi,\theta_1,\theta_2) & = &\sum_{i=1}^N\nolimits\ C_i\ \Phi_i(\phi)\ \Theta_{1i}(\theta_1)\ \Theta_{2i}(\theta_2)\\
\Phi_{i}(\phi)        & = &  u_i - \mathrm{cos}((\phi   - a_i)K_i) \\
\Theta_{1i}(\theta_1) & = &  v_i - \mathrm{cos}((\theta_1-b_i)L_i) \\
\Theta_{2i}(\theta_2) & = &  w_i - \mathrm{cos}((\theta_2-c_i)M_i)
\end{eqnarray*}

% Check using: http://quicklatex.com/  (24pt font)
\pagestyle{empty}
\end{document}

