Couple of questions about math

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So, the meme definition of a line I've seen is that it's the collection of all points between two points. And that this means that it's infinity points of zero length.
That doesn't really make a lot of sense to me.
If you pile up infinity zeroes, that's still 0. So how can that make a line?
Is there a better way of understanding a line?

2. Why don't we use a unit sphere and some kind of unit tetrahedron to make tetrahedronomy? (Like a 3D version of trigonometry, but using some kind of "right" tetrahedra.)