The Story of ‘X’

One of my favourite anecdotes from my days teaching in an English secondary school involves the variable x. I was introducing the concept of a linear equation. Specifically the y=mx+b that kids in Ontario learn all about in Grade 9.
I was explaining how you plot the line on a graph when a young boy got out of his chair threw his hand up and toward the board, palm open, indicating with a wild gesture the third last letter of the alphabet written plainly in the equation. “But Sir!” he exclaimed, “What Is X!”
For my students, up until this point a letter had represented some unknown quantity, and it was their responsibility to divine its value. To Solve For X! But this was a new concept. In y = 2x + 1, x isn’t a quantity to solve; it’s a variable, a symbol of all the possible numbers to which we could multiply by 2 and add 1. I was amused and did my best to explain the nuanced differences of this new concept masquerading as an old familiar one.
But how did X become the symbol of anything in the first place? Who was the mystery person who decided that we needed to use letters to represent numbers?
His name was François Viète.

François Viète

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