>
\[\begin{split}\begin{equation*}
 \begin{cases}
   \displaystyle a '' + \frac {1} {\beta ^ 2 \gamma} \gamma 'a' + \frac {1} {2 \beta ^ 2 \gamma} \gamma''a + ka - \frac { 2P} {(a + b)} - \frac {\epsilon_x ^ 2} {a ^ 3} = 0,
   \\
   \displaystyle b '' + \frac {1} {\beta ^ 2 \gamma} \gamma 'b' + \frac {1} {2 \beta ^ 2 \gamma} \gamma''b - kb - \frac { 2P} {(a + b)} - \frac {\epsilon_y ^ 2} {b ^ 3} = 0.
 \end{cases}
\end{equation*}\end{split}\]</div>
<p>Let <span class="math notranslate nohighlight"