Given line equation of 2-order:
$$9 x^{2} - 24 x y + 18 x + 16 y^{2} + 226 y + 209 = 0$$
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
$$a_{11} = 9$$
$$a_{12} = -12$$
$$a_{13} = 9$$
$$a_{22} = 16$$
$$a_{23} = 113$$
$$a_{33} = 209$$
To calculate the determinant
$$\Delta = \left|\begin{matrix}a_{11} & a_{12}\\a_{12} & a_{22}\end{matrix}\right|$$
or, substitute
$$\Delta = \left|\begin{matrix}9 & -12\\-12 & 16\end{matrix}\right|$$
$$\Delta = 0$$
Because
$$\Delta$$
is equal to 0, then
Rotate the resulting coordinate system by an angle φ
$$x' = \tilde x \cos{\left(\phi \right)} - \tilde y \sin{\left(\phi \right)}$$
$$y' = \tilde x \sin{\left(\phi \right)} + \tilde y \cos{\left(\phi \right)}$$
φ - determined from the formula
$$\cot{\left(2 \phi \right)} = \frac{a_{11} - a_{22}}{2 a_{12}}$$
substitute coefficients
$$\cot{\left(2 \phi \right)} = \frac{7}{24}$$
then
$$\phi = \frac{\operatorname{acot}{\left(\frac{7}{24} \right)}}{2}$$
$$\sin{\left(2 \phi \right)} = \frac{24}{25}$$
$$\cos{\left(2 \phi \right)} = \frac{7}{25}$$
$$\cos{\left(\phi \right)} = \sqrt{\frac{\cos{\left(2 \phi \right)}}{2} + \frac{1}{2}}$$
$$\sin{\left(\phi \right)} = \sqrt{1 - \cos^{2}{\left(\phi \right)}}$$
$$\cos{\left(\phi \right)} = \frac{4}{5}$$
$$\sin{\left(\phi \right)} = \frac{3}{5}$$
substitute coefficients
$$x' = \frac{4 \tilde x}{5} - \frac{3 \tilde y}{5}$$
$$y' = \frac{3 \tilde x}{5} + \frac{4 \tilde y}{5}$$
then the equation turns from
$$9 x'^{2} - 24 x' y' + 18 x' + 16 y'^{2} + 226 y' + 209 = 0$$
to
$$16 \left(\frac{3 \tilde x}{5} + \frac{4 \tilde y}{5}\right)^{2} - 24 \cdot \left(\frac{3 \tilde x}{5} + \frac{4 \tilde y}{5}\right) \left(\frac{4 \tilde x}{5} - \frac{3 \tilde y}{5}\right) + 226 \cdot \left(\frac{3 \tilde x}{5} + \frac{4 \tilde y}{5}\right) + 9 \left(\frac{4 \tilde x}{5} - \frac{3 \tilde y}{5}\right)^{2} + 18 \cdot \left(\frac{4 \tilde x}{5} - \frac{3 \tilde y}{5}\right) + 209 = 0$$
simplify
$$150 \tilde x + 25 \tilde y^{2} + 170 \tilde y + 209 = 0$$
$$\left(5 \tilde y + 17\right)^{2} = 80 - 150 \tilde x$$
$$\left(\tilde y + \frac{17}{5}\right)^{2} = \frac{16}{5} - 6 \tilde x$$
$$\tilde y'^{2} = \frac{16}{5} - 6 \tilde x$$
Given equation is by parabola
- reduced to canonical form
The center of the canonical coordinate system in OXY
$$x_{0} = \tilde x \cos{\left(\phi \right)} - \tilde y \sin{\left(\phi \right)}$$
$$y_{0} = \tilde x \sin{\left(\phi \right)} + \tilde y \cos{\left(\phi \right)}$$
$$x_{0} = 0 \cdot \frac{4}{5} + 0 \cdot \frac{3}{5}$$
$$y_{0} = 0 \cdot \frac{3}{5} + 0 \cdot \frac{4}{5}$$
$$x_{0} = 0$$
$$y_{0} = 0$$
The center of canonical coordinate system at point O
(0, 0)
Basis of the canonical coordinate system
$$\vec e_{1} = \left( \frac{4}{5}, \ \frac{3}{5}\right)$$
$$\vec e_{2} = \left( - \frac{3}{5}, \ \frac{4}{5}\right)$$