What is pi (π)?

Pi (written π) is the ratio between a circle's circumference and its diameter: divide the distance around any circle by the distance across it, through the center, and the answer is always π — about 3.14159, whatever the size of the circle.

π ≈ 3.14159265358979…

π is irrational: its decimal digits never repeat in a cycle and never end, which is why it is written as a symbol instead of a finite number. The digits above are deliberately kept short — long enough to be useful for a calculation, short enough that every digit here is certain.

O que fazer com isso

What pi is used for

Circle area (π×r²), circumference (2×π×r), and far beyond geometry — π shows up in probability, electronics, and wave equations because of its deep connection to circular and periodic motion.

Cuidado

Why 22/7 is not exactly pi

22/7 ≈ 3.142857 is a common rough approximation, close enough for quick estimates, but it is a fraction — and π is irrational, so no fraction equals it exactly.

Why does every circle share the same ratio?

Scale a circle up or down and both its circumference and diameter grow by the same factor, so their ratio stays fixed — that is the geometric reason π is a single universal constant rather than a different number for every circle.

Where does Pi Day come from?

March 14 is written 3/14 in the US date format, matching the first three digits of π — which is why Pi Day lands on that date rather than, say, July 22 (a nod to the 22/7 approximation, celebrated as Pi Approximation Day in some countries instead).