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x^2+y^2+z^2-xy+xz+yz+3x+3y-3z=0 canonical form

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 2    2    2                                        
x  + y  + z  - 3*z + 3*x + 3*y + x*z + y*z - x*y = 0
$$x^{2} - x y + x z + 3 x + y^{2} + y z + 3 y + z^{2} - 3 z = 0$$
x^2 - x*y + x*z + 3*x + y^2 + y*z + 3*y + z^2 - 3*z = 0
Invariants method
Given equation of the surface of 2-order:
$$x^{2} - x y + x z + 3 x + y^{2} + y z + 3 y + z^{2} - 3 z = 0$$
This equation looks like:
$$a_{11} x^{2} + 2 a_{12} x y + 2 a_{13} x z + 2 a_{14} x + a_{22} y^{2} + 2 a_{23} y z + 2 a_{24} y + a_{33} z^{2} + 2 a_{34} z + a_{44} = 0$$
where
$$a_{11} = 1$$
$$a_{12} = - \frac{1}{2}$$
$$a_{13} = \frac{1}{2}$$
$$a_{14} = \frac{3}{2}$$
$$a_{22} = 1$$
$$a_{23} = \frac{1}{2}$$
$$a_{24} = \frac{3}{2}$$
$$a_{33} = 1$$
$$a_{34} = - \frac{3}{2}$$
$$a_{44} = 0$$
The invariants of the equation when converting coordinates are determinants:
$$I_{1} = a_{11} + a_{22} + a_{33}$$
     |a11  a12|   |a22  a23|   |a11  a13|
I2 = |        | + |        | + |        |
     |a12  a22|   |a23  a33|   |a13  a33|

$$I_{3} = \left|\begin{matrix}a_{11} & a_{12} & a_{13}\\a_{12} & a_{22} & a_{23}\\a_{13} & a_{23} & a_{33}\end{matrix}\right|$$
$$I_{4} = \left|\begin{matrix}a_{11} & a_{12} & a_{13} & a_{14}\\a_{12} & a_{22} & a_{23} & a_{24}\\a_{13} & a_{23} & a_{33} & a_{34}\\a_{14} & a_{24} & a_{34} & a_{44}\end{matrix}\right|$$
$$I{\left(\lambda \right)} = \left|\begin{matrix}a_{11} - \lambda & a_{12} & a_{13}\\a_{12} & a_{22} - \lambda & a_{23}\\a_{13} & a_{23} & a_{33} - \lambda\end{matrix}\right|$$
     |a11  a14|   |a22  a24|   |a33  a34|
K2 = |        | + |        | + |        |
     |a14  a44|   |a24  a44|   |a34  a44|

     |a11  a12  a14|   |a22  a23  a24|   |a11  a13  a14|
     |             |   |             |   |             |
K3 = |a12  a22  a24| + |a23  a33  a34| + |a13  a33  a34|
     |             |   |             |   |             |
     |a14  a24  a44|   |a24  a34  a44|   |a14  a34  a44|

substitute coefficients
$$I_{1} = 3$$
     | 1    -1/2|   | 1   1/2|   | 1   1/2|
I2 = |          | + |        | + |        |
     |-1/2   1  |   |1/2   1 |   |1/2   1 |

$$I_{3} = \left|\begin{matrix}1 & - \frac{1}{2} & \frac{1}{2}\\- \frac{1}{2} & 1 & \frac{1}{2}\\\frac{1}{2} & \frac{1}{2} & 1\end{matrix}\right|$$
$$I_{4} = \left|\begin{matrix}1 & - \frac{1}{2} & \frac{1}{2} & \frac{3}{2}\\- \frac{1}{2} & 1 & \frac{1}{2} & \frac{3}{2}\\\frac{1}{2} & \frac{1}{2} & 1 & - \frac{3}{2}\\\frac{3}{2} & \frac{3}{2} & - \frac{3}{2} & 0\end{matrix}\right|$$
$$I{\left(\lambda \right)} = \left|\begin{matrix}1 - \lambda & - \frac{1}{2} & \frac{1}{2}\\- \frac{1}{2} & 1 - \lambda & \frac{1}{2}\\\frac{1}{2} & \frac{1}{2} & 1 - \lambda\end{matrix}\right|$$
     | 1   3/2|   | 1   3/2|   | 1    -3/2|
K2 = |        | + |        | + |          |
     |3/2   0 |   |3/2   0 |   |-3/2   0  |

     | 1    -1/2  3/2|   | 1   1/2   3/2 |   | 1   1/2   3/2 |
     |               |   |               |   |               |
K3 = |-1/2   1    3/2| + |1/2   1    -3/2| + |1/2   1    -3/2|
     |               |   |               |   |               |
     |3/2   3/2    0 |   |3/2  -3/2   0  |   |3/2  -3/2   0  |

$$I_{1} = 3$$
$$I_{2} = \frac{9}{4}$$
$$I_{3} = 0$$
$$I_{4} = - \frac{243}{16}$$
$$I{\left(\lambda \right)} = - \lambda^{3} + 3 \lambda^{2} - \frac{9 \lambda}{4}$$
$$K_{2} = - \frac{27}{4}$$
$$K_{3} = - \frac{81}{4}$$
Because
$$I_{3} = 0 \wedge I_{2} \neq 0 \wedge I_{4} \neq 0$$
then by type of surface:
you need to
Make the characteristic equation for the surface:
$$- I_{1} \lambda^{2} + I_{2} \lambda - I_{3} + \lambda^{3} = 0$$
or
$$\lambda^{3} - 3 \lambda^{2} + \frac{9 \lambda}{4} = 0$$
$$\lambda_{1} = \frac{3}{2}$$
$$\lambda_{2} = \frac{3}{2}$$
$$\lambda_{3} = 0$$
then the canonical form of the equation will be
$$\tilde z 2 \sqrt{\frac{\left(-1\right) I_{4}}{I_{2}}} + \left(\tilde x^{2} \lambda_{1} + \tilde y^{2} \lambda_{2}\right) = 0$$
and
$$- \tilde z 2 \sqrt{\frac{\left(-1\right) I_{4}}{I_{2}}} + \left(\tilde x^{2} \lambda_{1} + \tilde y^{2} \lambda_{2}\right) = 0$$
$$\frac{3 \tilde x^{2}}{2} + \frac{3 \tilde y^{2}}{2} + 3 \sqrt{3} \tilde z = 0$$
and
$$\frac{3 \tilde x^{2}}{2} + \frac{3 \tilde y^{2}}{2} - 3 \sqrt{3} \tilde z = 0$$
$$2 \tilde z + \left(\frac{\tilde x^{2}}{\sqrt{3}} + \frac{\tilde y^{2}}{\sqrt{3}}\right) = 0$$
and
$$- 2 \tilde z + \left(\frac{\tilde x^{2}}{\sqrt{3}} + \frac{\tilde y^{2}}{\sqrt{3}}\right) = 0$$
this equation is fora type elliptical paraboloid
- reduced to canonical form