After a short hiatus (mostly consisting of feeding a baby and cleaning up her poop), I thought I would come back to Ted Talk Tuesday with something on the lighter side. In this talk, Terry Moore explains how the letter “x” came to symbolize an unknown factor – not only in mathematics, but in many other arenas as well. By the time you get to the end, you will have the one sentence answer to the question: “Why is “x” the unknown?” And, like Terry Moore, I think it’s worth sharing.