
Pi 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. In manipulative 1, click on the blue points and drag them to change the circle. Note that for any size circle, the ratio of the circumference to the diameter remains constant. Pi is an irrational number. This means that the digits in the number go on forever without repeating. This 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. 
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