A lot of these conventions just develop according to what notation sticks, like how π caught on almost 3 millennia after the ratio was treated as a constant. A

A lot of these conventions just develop according to what notation sticks, like how π caught on almost 3 millennia after the ratio was treated as a constant. And not all of them are even as universal as one might think. mx+c is not. Charles Hutton used y = ax + b for the equation of a "right line" in xyr 1811 A Course of Mathematics, for example.