The Pythagorean Theorem tells us how the three sides of a right-angled triangle are related. It provides a vital link between geometry and algebra, allowing us to calculate distances in terms of coordinates. It also inspired trigonometry. It led to surveying, navigation, and more recently, special and general relativity—the best current theories of space, time, and gravity.
The Formula to Get 42 Billion Digits of π
While writing "7 Utterly Well-written Math Books About Pi," I found a very interesting math formula that will give you 42 consecutive digits of π accurately but is still wrong.