A very good explanation of how Newton applied calculus to come up with a much more efficient method of calculating pi (π). It starts with a nice illustration of the relationship between π and the area of a circle, moves explains the binomial theorem (quite nicely), and then shows how Newton generalized the binomial theorem to come up with an integral of a quarter of a unit circle. They don’t explain what a unit circle is, but that’s easy: it’s just a circle with a radius of 1.