This is LaTeX code:

[latex]
 
- p_2 \left[ \begin{array}{l}
 p\left( {1 - p} \right)\left( {1 - q} \right)\left[ {g_1 \left( {n_2 + 1} \right)g_1 \left( {n_1 } \right) + g_1 \left( {n_1 + 1} \right)g_1 \left( {n_2 } \right)} \right] + \\ 
 + p^2 g_1 \left( {n_1 } \right)g_1 \left( {n_2 } \right) \\ 
 \end{array} \right] =
 
[/latex]