ELI5: Explain Like I'm 5

31982 Johnwallis

So, have you ever heard of math? It's like when you count things, except it gets a lot trickier when you have to do really big numbers or do a lot of adding and subtracting.

Well, a long time ago there was a really smart man named John Wallis who was really, really good at math. One day, he came up with a new way to write down a number that was between three and four.

Instead of just writing 3 or 4, he wrote it like this: 3.1̅8̅1̅8̅2̅8̅2̅8̅2̅8̅...

That might look really confusing, but basically it's just a way to show that there are some numbers after the decimal point that go on forever and ever without repeating. That's called an "infinite decimal."

John Wallis was really clever, and he used this new kind of number to solve a lot of tricky math problems. For example, he used it to figure out how to measure the area of a circle.

So even though it might seem weird to write down a number that goes on forever, sometimes it can actually be really helpful!