Given line equation of 2-order:
$$3 x^{2} - 12 x - 6 y^{2} - 108 y - 492 = 0$$
This equation looks like:
$$a_{11} x^{2} + 2 a_{12} x y + 2 a_{13} x + a_{22} y^{2} + 2 a_{23} y + a_{33} = 0$$
where
$$a_{11} = 3$$
$$a_{12} = 0$$
$$a_{13} = -6$$
$$a_{22} = -6$$
$$a_{23} = -54$$
$$a_{33} = -492$$
The invariants of the equation when converting coordinates are determinants:
$$I_{1} = a_{11} + a_{22}$$
|a11 a12|
I2 = | |
|a12 a22|
$$I_{3} = \left|\begin{matrix}a_{11} & a_{12} & a_{13}\\a_{12} & a_{22} & a_{23}\\a_{13} & a_{23} & a_{33}\end{matrix}\right|$$
$$I{\left(\lambda \right)} = \left|\begin{matrix}a_{11} - \lambda & a_{12}\\a_{12} & a_{22} - \lambda\end{matrix}\right|$$
|a11 a13| |a22 a23|
K2 = | | + | |
|a13 a33| |a23 a33|
substitute coefficients
$$I_{1} = -3$$
|3 0 |
I2 = | |
|0 -6|
$$I_{3} = \left|\begin{matrix}3 & 0 & -6\\0 & -6 & -54\\-6 & -54 & -492\end{matrix}\right|$$
$$I{\left(\lambda \right)} = \left|\begin{matrix}3 - \lambda & 0\\0 & - \lambda - 6\end{matrix}\right|$$
|3 -6 | |-6 -54 |
K2 = | | + | |
|-6 -492| |-54 -492|
$$I_{1} = -3$$
$$I_{2} = -18$$
$$I_{3} = 324$$
$$I{\left(\lambda \right)} = \lambda^{2} + 3 \lambda - 18$$
$$K_{2} = -1476$$
Because
$$I_{2} < 0 \wedge I_{3} \neq 0$$
then by line type:
this equation is of type : hyperbola
Make the characteristic equation for the line:
$$- I_{1} \lambda + I_{2} + \lambda^{2} = 0$$
or
$$\lambda^{2} + 3 \lambda - 18 = 0$$
$$\lambda_{1} = 3$$
$$\lambda_{2} = -6$$
then the canonical form of the equation will be
$$\tilde x^{2} \lambda_{1} + \tilde y^{2} \lambda_{2} + \frac{I_{3}}{I_{2}} = 0$$
or
$$3 \tilde x^{2} - 6 \tilde y^{2} - 18 = 0$$
$$\frac{\tilde x^{2}}{6} - \frac{\tilde y^{2}}{3} = 1$$
- reduced to canonical form