CircumferenceDate: 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 r = radius and * 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. Glad to help! For more information about pi, see our Dr. Math FAQ at http://mathforum.org/dr.math/faq/ -Doctor Mason, The Math Forum Check out our web site! http://mathforum.org/dr.math/ |
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