ELI5: Explain Like I'm 5

Euler's formula

Euler's formula is like a secret code that helps us talk about really complicated math in a simpler way. It says that if you take a circle and draw a line from the center to the edge (that's like drawing a line from the middle of a pizza to the crust), you can use that line to help you figure out some really hard math problems.

The secret code is this:

e^ix = cos(x) + i*sin(x)

Okay, that looks really scary! But let's break it down.

The 'e' is a fancy number that's used a lot in math. It's like the number 10, except it's even better because it works with really tiny numbers too. It's like a superhero number that can do anything.

The 'i' is also a superhero number. It's a number that's not real like 1, 2, 3, or 4, but it's still really important. It's like a special kind of number that can do things that regular numbers can't.

The 'cos' and 'sin' are like little helpers that use the line we drew on the circle to help us figure out what the real answer is. They're like friends that help you understand something that's hard to figure out on your own.

So when we put all of these things together, Euler's formula tells us that if we take 'e' and raise it to the power of the imaginary number 'ix' (which is just a fancy way of talking about the line we drew on the circle), we'll get two new numbers: 'cos(x)' and 'i*sin(x)'.

These two new numbers have special meanings. The 'cos' number tells us how far away from the edge of the circle our line is, and the 'sin' number tells us how high up our line is from the center of the circle. By using these two numbers together, we can figure out all sorts of complicated math problems!

So that's Euler's formula. It's like a secret code that uses superheroes and helpers to make really hard math problems a lot easier to figure out!