What is Pi?Date: 03/02/97 at 22:51:41 From: Anna Subject: Pi's What exactly is pi? Is it a number, an equation, or what? Anna Date: 03/02/97 at 23:58:23 From: Doctor Mike Subject: Re: Pi's Dear Anna, Pi is a number. It is approximately equal to 3.1416 , but that is not its exact value. We are interested in this number because of an astounding fact about all circles. Take an exact circle, any circle. The distance around it is called the "circumference" and the length of a line from one side to the other through the center is called the "diameter". Sometimes that line itself is called a diameter line. Now divide: circumference --------------- = ? diameter What number do you get? For big circles or smaller circles or medium- sized circles the answer is ALWAYS the same. That number is pi. I cannot write down here for you exactly what pi is, because I would have to write down an infinite number of digits. I can tell you that a better approximate value is : 3.1415926535898 but that still is not exact. The real pi just keeps going on and on. Fortunately, most of the times we use it we only need one of the shorter approximate values for it. Two of the best known ways to use pi are in formulas for finding the circumference "C" of a circle and the area "A" of a circle, if you know what the radius "R" of the circle is. They are : C = 2*pi*R A = pi*R*R where "*" stands for multiplication. Since R*R is sometimes called "R squared", often this equation for area is said "pi R squared". In summary, pi is a number, but it is used in equations. -Doctor Mike, The Math Forum Check out our web site! http://mathforum.org/dr.math/ |
Search the Dr. Math Library: |
[Privacy Policy] [Terms of Use]
Ask Dr. Math^{TM}
© 1994- The Math Forum at NCTM. All rights reserved.
http://mathforum.org/dr.math/