On a humid Monday in late September, a wonky entrepreneur named Salman Khan visited New York City. Khan, a 35-year-old American of South Asian descent with bushy black hair and a nerdy affect, was in town to promote his Silicon Valley startup. He stayed at the London NYC, an upscale hotel just south of Central Park, and dined at Maze, the Gordon Ramsay restaurant off the lobby.
But that night, instead of seeing the sights or going out with friends, Khan holed up in his hotel room, fiddled with his laptop, and produced a series of amateurish videos about geometry. They are disarmingly simple – Khan’s deep voice talks over a black screen, where he draws shapes and writes out questions and equations in multiple colours. One, a six-minute clip called “Congruent triangle proof example”, shows a proof that a point on a line is the midpoint, using two triangles. Another, “Finding congruent triangles”, establishes why four related postulates are all equally reasonable. When he was finished, he uploaded them to YouTube and went to sleep.