quadratic equations in matrix form.

Hi

I'm sure this question will seem seem very trivial, but I was wondering if you could help me out.

Although I can see that quadratic equations such as

5x^2 -6xy+5y^2=8 can be shown as the matrix (xy)(5 -3/-3 5)=8 (Using the divide symbol to indicate row down.)

Similarly

7x^2-12xy-2y^2=10 would be (x y)(7 -6 /-6 -2)

but I was stuck when trying to convert the quadratic equation x^2 + x-8 +5xy -6y +2y^2=0 into matrix form.

If someone could shed some knowledge on the subject I would be deeply appreciative.

Thanks

Matt