Given line equation of 2-order:
$$14 x^{2} + 20 x y - 8 x - 7 y^{2} - 34 y - 35 = 0$$
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
$$a_{11} = 14$$
$$a_{12} = 10$$
$$a_{13} = -4$$
$$a_{22} = -7$$
$$a_{23} = -17$$
$$a_{33} = -35$$
To calculate the determinant
$$\Delta = \left|\begin{matrix}a_{11} & a_{12}\\a_{12} & a_{22}\end{matrix}\right|$$
or, substitute
$$\Delta = \left|\begin{matrix}14 & 10\\10 & -7\end{matrix}\right|$$
$$\Delta = -198$$
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
$$14 x_{0} + 10 y_{0} - 4 = 0$$
$$10 x_{0} - 7 y_{0} - 17 = 0$$
then
$$x_{0} = 1$$
$$y_{0} = -1$$
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
$$a'_{33} = - 4 x_{0} - 17 y_{0} - 35$$
$$a'_{33} = -22$$
then equation turns into
$$14 x'^{2} + 20 x' y' - 7 y'^{2} - 22 = 0$$
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
$$\cot{\left(2 \phi \right)} = \frac{21}{20}$$
then
$$\phi = \frac{\operatorname{acot}{\left(\frac{21}{20} \right)}}{2}$$
$$\sin{\left(2 \phi \right)} = \frac{20}{29}$$
$$\cos{\left(2 \phi \right)} = \frac{21}{29}$$
$$\cos{\left(\phi \right)} = \sqrt{\frac{\cos{\left(2 \phi \right)}}{2} + \frac{1}{2}}$$
$$\sin{\left(\phi \right)} = \sqrt{1 - \cos^{2}{\left(\phi \right)}}$$
$$\cos{\left(\phi \right)} = \frac{5 \sqrt{29}}{29}$$
$$\sin{\left(\phi \right)} = \frac{2 \sqrt{29}}{29}$$
substitute coefficients
$$x' = \frac{5 \sqrt{29} \tilde x}{29} - \frac{2 \sqrt{29} \tilde y}{29}$$
$$y' = \frac{2 \sqrt{29} \tilde x}{29} + \frac{5 \sqrt{29} \tilde y}{29}$$
then the equation turns from
$$14 x'^{2} + 20 x' y' - 7 y'^{2} - 22 = 0$$
to
$$- 7 \left(\frac{2 \sqrt{29} \tilde x}{29} + \frac{5 \sqrt{29} \tilde y}{29}\right)^{2} + 20 \left(\frac{2 \sqrt{29} \tilde x}{29} + \frac{5 \sqrt{29} \tilde y}{29}\right) \left(\frac{5 \sqrt{29} \tilde x}{29} - \frac{2 \sqrt{29} \tilde y}{29}\right) + 14 \left(\frac{5 \sqrt{29} \tilde x}{29} - \frac{2 \sqrt{29} \tilde y}{29}\right)^{2} - 22 = 0$$
simplify
$$18 \tilde x^{2} - 11 \tilde y^{2} - 22 = 0$$
$$- 18 \tilde x^{2} + 11 \tilde y^{2} + 22 = 0$$
Given equation is hyperbole
$$\frac{\tilde x^{2}}{\frac{11}{9}} - \frac{\tilde y^{2}}{2} = 1$$
- reduced to canonical form
The center of canonical coordinate system at point O
(1, -1)
Basis of the canonical coordinate system
$$\vec e_1 = \left( \frac{5 \sqrt{29}}{29}, \ \frac{2 \sqrt{29}}{29}\right)$$
$$\vec e_2 = \left( - \frac{2 \sqrt{29}}{29}, \ \frac{5 \sqrt{29}}{29}\right)$$