Definition: Pi is the constant ratio of any circle's circumference to its diameter, an irrational number approximately equal to 3.14159.
What is pi?
Pi, written with the Greek letter, is the number you get by dividing any circle’s circumference by its diameter. Small circle or huge circle, the answer is the same: about 3.14159.
What kind of number is it?
Pi is irrational. Its decimal never ends and never repeats. The fraction 22/7, about 3.1429, and 3.14 are only approximations.
How is it used?
Two formulas depend on it: C = pi d and A = pi r2. For a plate of diameter 26 cm, C = 3.14 x 26 = 81.64 cm. Leaving the answer as an exact multiple of pi, 26 pi cm, is also fine.
How do you measure it?
Wrap a string around a can and measure it. If the string is 22 cm and the can’s width is 7 cm, then 22 / 7 is about 3.14.
What is a common mistake?
Saying pi equals 3.14. That is a rounded value. When a problem says use 3.14, follow it. Otherwise your calculator’s pi key gives more accuracy.