What is π?

Abstract

There are many possible ways of introducing the number π, associated with the circle. We shall obtain π from the complex exponential function

$$ \exp \,z = 1 + \frac{z} {{2!}} + \cdots . $$

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And he made a molten sea, ten cubits from the one brim to the otherj it was round all about, and his height was five cubits, and a line of thirty cubits did compass it round about. (I Kings, Chapter 7, verse 23).