CALCULUS Understanding Its Concepts and Methods
Circle, Radius, Circumference, Area of circle
A circle
consists of all points that are fixed distance (the radius) from some point (the center).
The radius of a circle is the distance r from its center to any point on it. The diameter is the distance D across the circle, which is twice the radius.
D = 2r
The circumference of a circle is p times the diameter.
C = 2D = 2pr
The number p is approximately 3.1415926538979 .
The area of a circle is p times the square of its radius.
A = pr^{2}
Example: The circle with radius 5 has diameter D = 2 x 5 = 10 , circumference C = 10p ≈ 31.416 and area A = p × 5^{2} = 25p ≈ 78.54.
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Copyright © 2006 Darel Hardy, Fred Richman, Carol Walker, Robert Wisner. All rights reserved. Except upon the express prior permission in writing, from the authors, no part of this work may be reproduced, transcribed, stored electronically, or transmitted in any form by any method.