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.

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本文导出了平面螺管几何参数之间的关系及换热准则方程，并对这种换热器进行了设计计算和特点分析。

The relations between the geometric parameters, as well as the heat transfer criterion equations, of the plane spiral-tube are derived.

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以位置约束方程奇异性条件和结构参数空间复形剖分方法为基础，研究了平面机构尺度分类问题。

Based on singularity of constraint equation and complex division of structure-parameter-space, the dimension classification method of planar mechanism was researched.

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