$$
\mathbf{V}_1 \times \mathbf{V}_2 = \begin{vmatrix}
\mathbf{i} & \mathbf{j} & \mathbf{k} \
\frac{\partial X}{\partial u} & \frac{\partial Y}{\partial u} & 0 \
\frac{\partial X}{\partial v} & \frac{\partial Y}{\partial v} & 0 \
\end{vmatrix}
$$
$$x = {-b \pm \sqrt{b^2-4ac} \over 2a}$$
原文：https://www.cnblogs.com/zeng-zhi/p/10169834.html