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### Circumference

```
Date: 04/12/97 at 08:33:01
From: Chris Riley
Subject: Circumference

My class was trying to figure out the answer to this question.  What
is the circumference of a circle with a radius of 5.5?
```

```
Date: 04/12/97 at 15:48:25
From: Doctor Mason
Subject: Re: Circumference

Hi, Chris,

Most of the time we use a formula to calcuate the circumference of a
circle once either the radius or diameter is known.  To find the
circumference, you only need to multiply the diameter by a constant
known as pi.

Pi is approximately equal to the decimal 3.14 or the fraction 22/7.
Neither one of these values is exactly equal to pi, since pi is a
special kind of number (an irrational number), but even though 3.14
and 22/7 aren't exactly equal to pi, they are close enough to do most
calculations.

In the formulas below

C = circumference
d = diameter
* means multiply:

C = pi * d          or  since 2 radius equal a diameter,
C = pi * 2 * r      or often written
C = 2*pi*r

If you know that the radius = 5.5, then according to the last formula:

C = 2 * 3.14 * 5.5  =  34.54.

http://mathforum.org/dr.math/faq/

-Doctor Mason,  The Math Forum
Check out our web site!  http://mathforum.org/dr.math/
```
Associated Topics:
Elementary Circles
Elementary Geometry

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