*Macmillan Science Library: Mathematics*. Copyright © 2001-2006 by Macmillan Reference USA, an imprint of the Gale Group. All rights reserved.

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## What Is Pi?

What do the following items have in common with each other and all other circular figures: a quarter, approximately 1 inch across; a compact disc, 12 centimeters wide; a circular patio pool, spanning about 23 feet; and Earth's equator, roughly 8,000 miles in **diameter**. These estimated diameters are summarized in the table below, along with the estimated circumferences of the circular items.

In each case in the table, the circumference is about three times the diameter. The table also lists more precise measurements for the dimensions for our four examples. To determine the ratio of circumference (*c*) to its diameter (*d*), divide *c* by *d*. The resulting ratio of *c:d* is, in each case, a decimal slightly larger than 3.14. In fact, the circumference of *any* circle is about3.14 times larger than its diameter. The relation, then, between the diameter and circumference of a circle can be summarized algebraically as...

This section contains 1,409 words(approx. 5 pages at 300 words per page) |