This can be written in the quadratic form $\mathbf{x}^T A \mathbf{x} = 36$, where $\mathbf{x} = \begin{pmatrix} x \\ y \end{pmatrix}$ and $A$ is a symmetric matrix.
The general quadratic form is $ax^2 + bxy + cy^2$. In our case, $a=0$, $b=12$, $c=-5$.
The matrix
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