Given equation of the surface of 2-order:
− 6 x 1 x 2 + 3 x 1 x 3 = 0 - 6 x_{1} x_{2} + 3 x_{1} x_{3} = 0 − 6 x 1 x 2 + 3 x 1 x 3 = 0 This equation looks like:
a 11 x 3 2 + 2 a 12 x 2 x 3 + 2 a 13 x 1 x 3 + 2 a 14 x 3 + a 22 x 2 2 + 2 a 23 x 1 x 2 + 2 a 24 x 2 + a 33 x 1 2 + 2 a 34 x 1 + a 44 = 0 a_{11} x_{3}^{2} + 2 a_{12} x_{2} x_{3} + 2 a_{13} x_{1} x_{3} + 2 a_{14} x_{3} + a_{22} x_{2}^{2} + 2 a_{23} x_{1} x_{2} + 2 a_{24} x_{2} + a_{33} x_{1}^{2} + 2 a_{34} x_{1} + a_{44} = 0 a 11 x 3 2 + 2 a 12 x 2 x 3 + 2 a 13 x 1 x 3 + 2 a 14 x 3 + a 22 x 2 2 + 2 a 23 x 1 x 2 + 2 a 24 x 2 + a 33 x 1 2 + 2 a 34 x 1 + a 44 = 0 where
a 11 = 0 a_{11} = 0 a 11 = 0 a 12 = 0 a_{12} = 0 a 12 = 0 a 13 = 3 2 a_{13} = \frac{3}{2} a 13 = 2 3 a 14 = 0 a_{14} = 0 a 14 = 0 a 22 = 0 a_{22} = 0 a 22 = 0 a 23 = − 3 a_{23} = -3 a 23 = − 3 a 24 = 0 a_{24} = 0 a 24 = 0 a 33 = 0 a_{33} = 0 a 33 = 0 a 34 = 0 a_{34} = 0 a 34 = 0 a 44 = 0 a_{44} = 0 a 44 = 0 The invariants of the equation when converting coordinates are determinants:
I 1 = a 11 + a 22 + a 33 I_{1} = a_{11} + a_{22} + a_{33} I 1 = a 11 + a 22 + a 33 |a11 a12| |a22 a23| |a11 a13|
I2 = | | + | | + | |
|a12 a22| |a23 a33| |a13 a33| I 3 = ∣ a 11 a 12 a 13 a 12 a 22 a 23 a 13 a 23 a 33 ∣ 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 3 = a 11 a 12 a 13 a 12 a 22 a 23 a 13 a 23 a 33 I 4 = ∣ 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 ∣ 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 4 = 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 I ( λ ) = ∣ a 11 − λ a 12 a 13 a 12 a 22 − λ a 23 a 13 a 23 a 33 − λ ∣ 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| I ( λ ) = a 11 − λ a 12 a 13 a 12 a 22 − λ a 23 a 13 a 23 a 33 − λ |a11 a14| |a22 a24| |a33 a34|
K2 = | | + | | + | |
|a14 a44| |a24 a44| |a34 a44| |a11 a12 a14| |a22 a23 a24| |a11 a13 a14|
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K3 = |a12 a22 a24| + |a23 a33 a34| + |a13 a33 a34|
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|a14 a24 a44| |a24 a34 a44| |a14 a34 a44| substitute coefficients
I 1 = 0 I_{1} = 0 I 1 = 0 |0 0| |0 -3| | 0 3/2|
I2 = | | + | | + | |
|0 0| |-3 0 | |3/2 0 | I 3 = ∣ 0 0 3 2 0 0 − 3 3 2 − 3 0 ∣ I_{3} = \left|\begin{matrix}0 & 0 & \frac{3}{2}\\0 & 0 & -3\\\frac{3}{2} & -3 & 0\end{matrix}\right| I 3 = 0 0 2 3 0 0 − 3 2 3 − 3 0 I 4 = ∣ 0 0 3 2 0 0 0 − 3 0 3 2 − 3 0 0 0 0 0 0 ∣ I_{4} = \left|\begin{matrix}0 & 0 & \frac{3}{2} & 0\\0 & 0 & -3 & 0\\\frac{3}{2} & -3 & 0 & 0\\0 & 0 & 0 & 0\end{matrix}\right| I 4 = 0 0 2 3 0 0 0 − 3 0 2 3 − 3 0 0 0 0 0 0 I ( λ ) = ∣ − λ 0 3 2 0 − λ − 3 3 2 − 3 − λ ∣ I{\left(\lambda \right)} = \left|\begin{matrix}- \lambda & 0 & \frac{3}{2}\\0 & - \lambda & -3\\\frac{3}{2} & -3 & - \lambda\end{matrix}\right| I ( λ ) = − λ 0 2 3 0 − λ − 3 2 3 − 3 − λ |0 0| |0 0| |0 0|
K2 = | | + | | + | |
|0 0| |0 0| |0 0| |0 0 0| |0 -3 0| | 0 3/2 0|
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K3 = |0 0 0| + |-3 0 0| + |3/2 0 0|
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|0 0 0| |0 0 0| | 0 0 0| I 1 = 0 I_{1} = 0 I 1 = 0 I 2 = − 45 4 I_{2} = - \frac{45}{4} I 2 = − 4 45 I 3 = 0 I_{3} = 0 I 3 = 0 I 4 = 0 I_{4} = 0 I 4 = 0 I ( λ ) = − λ 3 + 45 λ 4 I{\left(\lambda \right)} = - \lambda^{3} + \frac{45 \lambda}{4} I ( λ ) = − λ 3 + 4 45 λ K 2 = 0 K_{2} = 0 K 2 = 0 K 3 = 0 K_{3} = 0 K 3 = 0 Because
I 3 = 0 ∧ I 4 = 0 ∧ I 2 ≠ 0 I_{3} = 0 \wedge I_{4} = 0 \wedge I_{2} \neq 0 I 3 = 0 ∧ I 4 = 0 ∧ I 2 = 0 then by type of surface:
you need to
Make the characteristic equation for the surface:
− I 1 λ 2 + I 2 λ − I 3 + λ 3 = 0 - I_{1} \lambda^{2} + I_{2} \lambda - I_{3} + \lambda^{3} = 0 − I 1 λ 2 + I 2 λ − I 3 + λ 3 = 0 or
λ 3 − 45 λ 4 = 0 \lambda^{3} - \frac{45 \lambda}{4} = 0 λ 3 − 4 45 λ = 0 λ 1 = − 3 5 2 \lambda_{1} = - \frac{3 \sqrt{5}}{2} λ 1 = − 2 3 5 λ 2 = 3 5 2 \lambda_{2} = \frac{3 \sqrt{5}}{2} λ 2 = 2 3 5 λ 3 = 0 \lambda_{3} = 0 λ 3 = 0 then the canonical form of the equation will be
( x ~ 2 2 λ 2 + x ~ 3 2 λ 1 ) + K 3 I 2 = 0 \left(\tilde x2^{2} \lambda_{2} + \tilde x3^{2} \lambda_{1}\right) + \frac{K_{3}}{I_{2}} = 0 ( x ~ 2 2 λ 2 + x ~ 3 2 λ 1 ) + I 2 K 3 = 0 3 5 x ~ 2 2 2 − 3 5 x ~ 3 2 2 = 0 \frac{3 \sqrt{5} \tilde x2^{2}}{2} - \frac{3 \sqrt{5} \tilde x3^{2}}{2} = 0 2 3 5 x ~ 2 2 − 2 3 5 x ~ 3 2 = 0 − x ~ 2 2 ( 5 3 4 6 15 ) 2 + x ~ 3 2 ( 5 3 4 6 15 ) 2 = 0 - \frac{\tilde x2^{2}}{\left(\frac{5^{\frac{3}{4}} \sqrt{6}}{15}\right)^{2}} + \frac{\tilde x3^{2}}{\left(\frac{5^{\frac{3}{4}} \sqrt{6}}{15}\right)^{2}} = 0 − ( 15 5 4 3 6 ) 2 x ~ 2 2 + ( 15 5 4 3 6 ) 2 x ~ 3 2 = 0 this equation is fora type two intersecting planes
- reduced to canonical form