The circumference (perimeter) of a circle is given by the formula
C = 2 (pi) (r), where r is the radius. Since radius is half of the diameter, d = 2 (r), so C = (pi) d.
Dividing both sides by d to get pi by itself, pi is the circumference of a circle divided by the diameter.
Pi is irrational, meaning that it goes on forever, without repeating numbers and cannot be represented as a fraction.
In everyday life, we often use 22/7 as an approximation of pi. Other people use 3.14.
I have memorized what my calculator gave me plus one more decimal, 3.1415926536.
Others have memorized it to thousands of digits and people have spent their lifetimes calculating pi to more and more decimals. Books have been written about pi.
Some schools celebrate Pi Day, since Pi begins with 3.14, it is celebrated on March 14th.
Good luck,
Paul
https://en.wikipedia.org/wiki/Pi
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