# Pi

Pronunciation: /paɪ/ Explain
 Click on the blue point and drag it to change the figure. Is there any case where the ratio of the circumference of a circle to its diameter is not pi? Manipulative 1 - Definition of π (pi) Created with GeoGebra.

Pi (π) is a constant. It is defined to be the ratio of the circumference of a circle to the diameter. The symbol for pi is the Greek letter π. The value of pi is approximately 3.14159.

Pi is an irrational number. This means that the digits in the number go on forever without repeating. This also means that no one can know the exact value of pi. In the past, some mathematicians have used the fraction 22 / 7 to approximate pi. This approximation is accurate to 3 decimal places.

### References

1. McAdams, David E.. All Math Words Dictionary, pi. 2nd Classroom edition 20150108-4799968. pg 138. Life is a Story Problem LLC. January 8, 2015. Buy the book

McAdams, David E. Pi. 4/27/2019. All Math Words Encyclopedia. Life is a Story Problem LLC. https://www.allmathwords.org/en/p/pi.html.

### Revision History

4/27/2019: Changed equations and expressions to new format. (McAdams, David E.)
12/21/2018: Reviewed and corrected IPA pronunication. (McAdams, David E.)