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Pi (π)
The ratio of any circle's circumference to its diameter. Always 3.14159… and never settles.
Roll a circle to find π
Roll once around — the distance covered is π × diameter.
0.79d
1.57d
2.36d
3.14d
π ≈ 3.14159…
Distance rolled = π × diameter. The ratio is the same for every circle.
π — the digits never settle
Pi's decimal expansion is irrational. No pattern, no repeat, no end.
3.1415926535897
Why π?
Take any circle. Measure all the way around (the circumference) and across the middle (the diameter). Divide one by the other. You always get the same number — about 3.14. That number is π.