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.

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