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The number pi = 3.1415927...


The number pi is equal to 3.1415927 seven places after the decimal point.

It is commonly used when calculating the circumference and the area of a circle, which formulas are equal to

2 × π × r and π × r2    respectively

Ever wondered where pi came from or why pi is equal to 3.1415927?

let's us do an experiment:

Take any piece of string. Use a ruler to measure the length of the string in inches or centimeters or any units you want

string-image

Write down the length of the string on a piece of paper.

Now play with the string until you make a circle with it. Then, use a ruler to measure the diameter of the circle.

string-image

Write down the length of the diameter on a piece of paper.

Do a ratio of the circumference to the diameter

You should find something very close to 3.1415927.

The piece of string you see on the picture above has a length of about 22 inches and I found a diameter of 7 inches. 22 divided by 7 is equal to 3.142857143.

It is not equal exactly to 3.1415927, but it is ok because in practice we use 3.14 to do calculation. All we needed here was a good approximation.

Repeat the experiment above with a longer or a shorter piece of string. You should find a similar answer for pi because the size for the circle does not matter.

In general, regardless of the size of the circle, the following is always true.

string-image

From the formula above, you can see that C = π ×D = pi ×D

Since D = 2 × r, C = 2 × π × r


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