Given line equation of 2-order:
$$8 x^{2} + 15 x + 5 y^{2} + 6 y - 7 = 0$$
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
$$a_{11} = 8$$
$$a_{12} = 0$$
$$a_{13} = \frac{15}{2}$$
$$a_{22} = 5$$
$$a_{23} = 3$$
$$a_{33} = -7$$
To calculate the determinant
$$\Delta = \left|\begin{matrix}a_{11} & a_{12}\\a_{12} & a_{22}\end{matrix}\right|$$
or, substitute
$$\Delta = \left|\begin{matrix}8 & 0\\0 & 5\end{matrix}\right|$$
$$\Delta = 40$$
Because
$$\Delta$$
is not equal to 0, then
find the center of the canonical coordinate system. To do it, solve the system of equations
$$a_{11} x_{0} + a_{12} y_{0} + a_{13} = 0$$
$$a_{12} x_{0} + a_{22} y_{0} + a_{23} = 0$$
substitute coefficients
$$8 x_{0} + \frac{15}{2} = 0$$
$$5 y_{0} + 3 = 0$$
then
$$x_{0} = - \frac{15}{16}$$
$$y_{0} = - \frac{3}{5}$$
Thus, we have the equation in the coordinate system O'x'y'
$$a'_{33} + a_{11} x'^{2} + 2 a_{12} x' y' + a_{22} y'^{2} = 0$$
where
$$a'_{33} = a_{13} x_{0} + a_{23} y_{0} + a_{33}$$
or
$$a'_{33} = \frac{15 x_{0}}{2} + 3 y_{0} - 7$$
$$a'_{33} = - \frac{2533}{160}$$
then equation turns into
$$8 x'^{2} + 5 y'^{2} - \frac{2533}{160} = 0$$
Given equation is ellipse
$$\frac{\tilde x^{2}}{\left(\frac{\sqrt{12665}}{80}\right)^{2}} + \frac{\tilde y^{2}}{\left(\frac{\sqrt{5066}}{40}\right)^{2}} = 1$$
- reduced to canonical form
The center of canonical coordinate system at point O
-15
(----, -3/5)
16
Basis of the canonical coordinate system
$$\vec e_{1} = \left( 1, \ 0\right)$$
$$\vec e_{2} = \left( 0, \ 1\right)$$