*The *Pythagorean Theorem* tells us h*ow 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 s*urveying, 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.