Originally Posted by

**symmetry** I was not talking about displacement. Displacement is a physics concept.

I am more interested in pure mathematics. Although, physics goes deep into math formulas and concepts, especially as used in astronomy.

I said there is a distance formula like this: D = rt

and then there is another distance formula used to measure the distance between (x,y) points on the xy-plane and this is what it looks like:

D = sqrt({x2 - x1)^2 + (y2 - y1)^2}).

Why are they BOTH called distance?

Thanks.