Considering I never saw a mathematical equation involve words, what possessed those numerically privileged (no, not $) to use x and y as variables. Why not just 'a' or 'b'? Sure those are used but not as much as 'x' and 'y'. If I was doing operations on text comparison I can see why bc letter frequency factors into ease. So, the letters 'q' and 'z' would be good variable choices.
Does anyone really know how x and y came to convention?