Is a straight line yang

Answer 1

I don't think there's a strict mathematical definition. A straight line is one of those elementary geometric objects (along with terms like point, angle, distance, etc) that are assumed to exist, out of which other figures may be constructed.

You could say "shortest distance between points," but that doesn't necessarily convey the notion of "straight" - especially in non-euclidean geometries where geodesics may be curved - nor imply the (usually) infinite extent of a line. Without actually defining "line," we agree that if all the points belong to the same line then they are co-linear, which we then call "straight." At least that's how I think it works.

Algebracially you can define a straight line in terms of relations among the coordinates of each point. Of course you first have to establish coordinate axes, which are all assumed to be straight lines. So that approach seems shaky, too, lol.

In the physical world we can define "straight" as "the path that light takes," though it's still a slippery concept with much to quibble about.

Answer 2

Yes, it has to be straight or it is not a line.

Answer 3

yes verticle is up and down

Answer 4

oblong