" The study of algebra in its own right, as a symbolic system apart from its applications, began to flourish in Renaissance Europe. It reached its pinnacle in the 1500s, when it started to look like what we know today, with letters used to represent numbers. In France in 1591, François Viète designated unknown quantities with vowels, like A and E, and used consonants, like B and G, for constants. (Today’s use of x, y, z for unknowns and a, b, c for constants came from the work of René Descartes about fifty years later.) Replacing words with letters and symbols made it much easier to manipulate equations and find solutions. "

― Steven H. Strogatz , Infinite Powers: How Calculus Reveals the Secrets of the Universe