Find the linearization $L \left( x, y \right)$ of the function $f\left( x, y \right) = \sqrt{ 161 - 9 x^{2} - 4 y^{2} }$ at $\left( -4, -2 \right)$.

$L \left( x, y \right) =$

Note: Your answer should be an expression in x and y; e.g. "3x - 5y + 9"