把向量外积定义为： |a ×b| = |a|·|b|·Sin
当然也有另一种方法，就是用参数方程表示这两条直线，用两条直线的方向向量作外积，从而得到切平面的法向量。
Another way to do it, of course, would provide actually parametric equations of these lines, get vectors along them and then take the cross-product to get the normal vector to the plane.
第一章是向量代数，主要介绍向量的线性运算、向量的内积、向量的外积、向量的混合积和双重外积。
The first chapter is about vector algebra, introduces the vector of linear operations, inner product of vectors, vector outer product, vector product and double mixed exterior product.
然后由平埘的点法式方程自然地引出了用坐标法定义向量的内积外积。
Then, we prove that the definition of coordinate method and that of vector method are equivalent.
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