X marks the unknown in algebra – but X's origins are a math mystery

How did the letter x get its enduring role as a symbol of the unknown? A mathematician explains why it’s hard to say for sure.

A Most Elegant Equation - Euler's Formula and The Beauty of Mathematics (PDFDrive), PDF, Mathematics

The Conversation

History – News, Research and Analysis – The Conversation – page 6

Mathematics – information, recherche et analyse – La Conversation

Unknown Number in an Equation Mixed Up Puzzles Printable & Digital (Google) - The Owl Teacher

Use of X As Unknown in Algebra Explained

Innovation and Certainty

Mathematics – information, recherche et analyse – La Conversation

Mathstodon

GK Reporter - News and Magazine Joomla Template

A Brief History of “X” – Mashed Radish

FactCheck.org — LiveJournal

Be Smart, How Did X Become the Unknown (and so much else)?, Season 11, Episode 17