Focusing on its definition:
* Pi is the ratio of a circle's circumference to its diameter. (Simple and accurate)
* Pi, an irrational number, is represented by the Greek letter π and approximately equals 3.14159. (More detailed and technical)
Focusing on its usage:
* To calculate the area of a circle, you multiply pi by the square of the radius. (Practical application)
* The value of pi is fundamental in many mathematical and scientific calculations. (Highlights its importance)
Using a playful or creative approach:
* Pi, the never-ending number, always keeps us on our toes. (A bit poetic)
* Pi is a mathematical mystery that has fascinated mathematicians for centuries. (Intriguing and emphasizes its enduring appeal)
Ultimately, the best sentence for pi depends on your intended audience and purpose.