第6章 6.22

$u = \begin{vmatrix} 1 & 1 & 1 \\ x & y & z \\ x^2 & y^2 & z^2 \end{vmatrix} = yz^2 + x^2z + xy^2 - yx^2 - xz^2 - y^2z$

$\Delta u = (2xz + y^2 - 2xy - z^2) + (z^2 + 2xy - x^2 - 2yz) + (2yz + x^2 - 2xz - y^2)$

$= 2z - 2y + 2x - 2z + 2y - 2x = 0$