Given line equation of 2-order:
$$3 x^{2} - \frac{173 x y}{50} + 5 y^{2} - 6 = 0$$
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
$$a_{11} = 3$$
$$a_{12} = - \frac{173}{100}$$
$$a_{13} = 0$$
$$a_{22} = 5$$
$$a_{23} = 0$$
$$a_{33} = -6$$
To calculate the determinant
$$\Delta = \left|\begin{matrix}a_{11} & a_{12}\\a_{12} & a_{22}\end{matrix}\right|$$
or, substitute
$$\Delta = \left|\begin{matrix}3 & - \frac{173}{100}\\- \frac{173}{100} & 5\end{matrix}\right|$$
$$\Delta = \frac{120071}{10000}$$
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
$$3 x_{0} - \frac{173 y_{0}}{100} = 0$$
$$- \frac{173 x_{0}}{100} + 5 y_{0} = 0$$
then
$$x_{0} = 0$$
$$y_{0} = 0$$
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
$$a'_{33} = -6$$
$$a'_{33} = -6$$
then equation turns into
$$3 x'^{2} - \frac{173 x' y'}{50} + 5 y'^{2} - 6 = 0$$
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
$$\cot{\left(2 \phi \right)} = \frac{100}{173}$$
then
$$\phi = \frac{\operatorname{acot}{\left(\frac{100}{173} \right)}}{2}$$
$$\sin{\left(2 \phi \right)} = \frac{173 \sqrt{39929}}{39929}$$
$$\cos{\left(2 \phi \right)} = \frac{100 \sqrt{39929}}{39929}$$
$$\cos{\left(\phi \right)} = \sqrt{\frac{\cos{\left(2 \phi \right)}}{2} + \frac{1}{2}}$$
$$\sin{\left(\phi \right)} = \sqrt{1 - \cos^{2}{\left(\phi \right)}}$$
$$\cos{\left(\phi \right)} = \sqrt{\frac{50 \sqrt{39929}}{39929} + \frac{1}{2}}$$
$$\sin{\left(\phi \right)} = \sqrt{\frac{1}{2} - \frac{50 \sqrt{39929}}{39929}}$$
substitute coefficients
$$x' = \tilde x \sqrt{\frac{50 \sqrt{39929}}{39929} + \frac{1}{2}} - \tilde y \sqrt{\frac{1}{2} - \frac{50 \sqrt{39929}}{39929}}$$
$$y' = \tilde x \sqrt{\frac{1}{2} - \frac{50 \sqrt{39929}}{39929}} + \tilde y \sqrt{\frac{50 \sqrt{39929}}{39929} + \frac{1}{2}}$$
then the equation turns from
$$3 x'^{2} - \frac{173 x' y'}{50} + 5 y'^{2} - 6 = 0$$
to
$$5 \left(\tilde x \sqrt{\frac{1}{2} - \frac{50 \sqrt{39929}}{39929}} + \tilde y \sqrt{\frac{50 \sqrt{39929}}{39929} + \frac{1}{2}}\right)^{2} - \frac{173 \left(\tilde x \sqrt{\frac{1}{2} - \frac{50 \sqrt{39929}}{39929}} + \tilde y \sqrt{\frac{50 \sqrt{39929}}{39929} + \frac{1}{2}}\right) \left(\tilde x \sqrt{\frac{50 \sqrt{39929}}{39929} + \frac{1}{2}} - \tilde y \sqrt{\frac{1}{2} - \frac{50 \sqrt{39929}}{39929}}\right)}{50} + 3 \left(\tilde x \sqrt{\frac{50 \sqrt{39929}}{39929} + \frac{1}{2}} - \tilde y \sqrt{\frac{1}{2} - \frac{50 \sqrt{39929}}{39929}}\right)^{2} - 6 = 0$$
simplify
$$- \frac{173 \tilde x^{2} \sqrt{\frac{1}{2} - \frac{50 \sqrt{39929}}{39929}} \sqrt{\frac{50 \sqrt{39929}}{39929} + \frac{1}{2}}}{50} - \frac{100 \sqrt{39929} \tilde x^{2}}{39929} + 4 \tilde x^{2} - \frac{346 \sqrt{39929} \tilde x \tilde y}{39929} + 4 \tilde x \tilde y \sqrt{\frac{1}{2} - \frac{50 \sqrt{39929}}{39929}} \sqrt{\frac{50 \sqrt{39929}}{39929} + \frac{1}{2}} + \frac{100 \sqrt{39929} \tilde y^{2}}{39929} + \frac{173 \tilde y^{2} \sqrt{\frac{1}{2} - \frac{50 \sqrt{39929}}{39929}} \sqrt{\frac{50 \sqrt{39929}}{39929} + \frac{1}{2}}}{50} + 4 \tilde y^{2} - 6 = 0$$
$$- \frac{\sqrt{39929} \tilde x^{2}}{100} + 4 \tilde x^{2} + \frac{\sqrt{39929} \tilde y^{2}}{100} + 4 \tilde y^{2} - 6 = 0$$
Given equation is ellipse
$$\frac{\tilde x^{2}}{\left(\frac{1}{\frac{\sqrt{6}}{6} \sqrt{4 - \frac{\sqrt{39929}}{100}}}\right)^{2}} + \frac{\tilde y^{2}}{\left(\frac{1}{\frac{\sqrt{6}}{6} \sqrt{\frac{\sqrt{39929}}{100} + 4}}\right)^{2}} = 1$$
- reduced to canonical form
The center of canonical coordinate system at point O
(0, 0)
Basis of the canonical coordinate system
$$\vec e_1 = \left( \sqrt{\frac{50 \sqrt{39929}}{39929} + \frac{1}{2}}, \ \sqrt{\frac{1}{2} - \frac{50 \sqrt{39929}}{39929}}\right)$$
$$\vec e_2 = \left( - \sqrt{\frac{1}{2} - \frac{50 \sqrt{39929}}{39929}}, \ \sqrt{\frac{50 \sqrt{39929}}{39929} + \frac{1}{2}}\right)$$