并且这个平面包含了原点和动点，以及速度矢量。

And, that's the plane that contains the origin, the point, and the velocity vector.

youdao

我们来看中间的那个点，在原点上，那就是一个鞍点，在这点做一个切平面,你可以看到这个切平面,是在原点上水平的。

See the point in the middle, at the origin, is a saddle point. If you look at the tangent plane to this graph, you will see that it is actually horizontal at the origin.

youdao

因为所有的平面都过原点。

Well, that's because all of your planes have to pass through the origin.

youdao

That's the plane with some origin here.

这是一个平面,这里是原点

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