[piytar]

Here is one use of pi, e (another transcendental number, namely the base of the natural logarithm aka Euler’s number) and i (the square root of -1) that I still find to be incredible:

e^(i*pi) = -1

/yes, geek mode here

[Mr. K]

I was blown away when I first learned that
d/dx (e^x) = e^x

[Talisker]

Here is one use of pi, e (another transcendental number, namely the base of the natural logarithm aka Euler’s number) and i (the square root of -1) that I still find to be incredible: e^(i*pi) = -1

Yeah, contemplating that one... makes you believe in The Force.