ELI5: Explain Like I'm 5

Cauchy–Riemann equations

Okay, so you know how numbers can be real or imaginary, right? Well, complex numbers are a little bit of both! They have a "real" part and an "imaginary" part.

Now, imagine you have a function that takes in a complex number and spits out another complex number. The Cauchy-Riemann equations tell us something really cool about that function.

Basically, the equations say that if the function is "nice" (meaning it's smooth and stuff), then it has to follow a certain pattern. Specifically, if you take the first partial derivative of the function with respect to the real part of the input, and then take the second partial derivative with respect to the imaginary part, you should get the negative of the other way around.

This might sound confusing, but it's actually really important for lots of complicated math stuff. Basically, it helps us understand how complex functions behave and how we can use them to solve math problems. Pretty cool, huh?