Why is 'x' the symbol for an unknown? In this short and funny talk, Terry Moore gives the surprising answer.

Archaeology from space | Sarah Parcak

What should future schools look like? How do brains learn? Some of the world's greatest educators, researchers, and community leaders share their stories and visions onstage at the TED conference, TEDx events and partner events around the world. You can also download these and many other videos free on TED.com, with an interactive English transcript and subtitles in up to 80 languages. TED is a nonprofit devoted to Ideas Worth Spreading.