我们用两个方程来描述一条直线,两个方程告诉我们平面相交于直线。

So, we could describe a line by two equations telling us about the two planes that intersect on the line.

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这个两平面相交得到的直线，两平面都经过同一条直线，此处，另外两平面交成直线，这一条，那一条。

So, see, the lines of intersections between two of the planes, so, here they all pass through the same line, and here, instead, they intersect in one line here, one line here, and one line there.

youdao

这样的2维宇宙模型就像是球体，不可能出现平行的测地线(测地线是曲面上的直线)——两直线必然在某点相交。

A two-dimensional model of such a universe would look like a sphere. It's impossible to have parallel geodesics (straight lines on a curved surface) — the two lines will cross at some point.

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