Professor Strang explains how the “magic number e” connects to ordinary things like the interest on a bank account. The graph of
y = e^x has the special property that its slope equals its height (it goes up “exponentially fast”!). This is the great function of calculus.

Professor Strang’s Calculus textbook (1st edition, 1991) is freely available here.

Subtitles are provided through the generous assistance of Jimmy Ren.