# Why does (h,k) generally represent the center of a circle?

Why are h and k generally used to denote the coordinates of the center of a circle?

After a bit of research, we found that h may represent "horizontal shift" or "horizontal translation", but we're not sure, and we can't figure out what k represents.

Thanks!

• This MetaFilter question is related to this one. Note that someone said it was about alphabetical progression, so from $h$, people went to $i$ and skipped it because imaginary numbers, people went to $j$ and skipped it because imaginary numbers in engineering, and then settled on $k$. Commented May 19, 2016 at 20:42
• Ok, that seems possible. Is there any evidence for that? Thanks! Commented May 19, 2016 at 20:44
• It was just a conjecture someone wrote on MetaFilter, but they did not give any evidence. Commented May 19, 2016 at 20:45
• I find odd that one contests that this is standard notation. In my experience much more common is $(x_0, y_0)$ or $(a,b)$. Commented May 19, 2016 at 20:47