A marvellous article on #pi
and where it comes from, why it keeps cropping up, and why so often found together with e. Recommended for #maths
"So here, again, is the exponential function, stemming from its unique property as the fixed point of the operator 𝑑/𝑑𝑥. And here, again, is our friend 𝜋, always accompanying its master of which it is the period (times 2𝑖). And this, finally, is where #𝜋
comes from, and what it is, and there are no circles to be found."
Alon Amit's answer to What is [math]\pi[/math]? - Quorawww.quora.com