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.

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。

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Since normal plastic theory is too complex, the membrane theory and the semi-membrane theory are adopted to establish the equilibrlm equations in plastic limit analysis.

鉴于有矩理论的复杂性，本文在作极限分析时，采用了无矩理论和半无矩理论的平衡方程分别作为中短壳和长壳的平衡方程。

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Very general systems of differential equations can be reduced to the normal form.

形式很普通的微分方程组可以化为正规的形式。

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