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2 2 = r2 This is the standard form of the equation of a circle with radius r and center ( h, k ) . Example 1 Write down the equation of a circle with radius 8 and center ( 4,7 ) .
Solution
Okay, in this case we have r = 8 , h = 4 and k = 7 so all we need to do is plug them into the
standard form of the equation of the circle. ( x  ( 4 ) ) + ( y  7 ) 2 = 82 ( x + 4) + ( y  7 ) 2 = 64 2
2 Do not square out the two terms on the left. Leaving these terms as they are will allow us to
quickly identify the equation as that of a circle and to quickly identify the radius and center of the
circle.
Graphing circles is a fairly simple process once we know the radius and center. In order to graph
a circle all we really need is the right most, left most, top most and bottom most points on the
circle. Once we know these it’s easy to sketch in the circle. © 2007 Paul Dawkins 169 http://tutorial.math.lamar.edu/terms.aspx College Algebra Nicely enough for us these points are easy to find. Since these are points on the circle we know
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This note was uploaded on 06/06/2012 for the course ICT 4 taught by Professor Mrvinh during the Spring '12 term at Hanoi University of Technology.
 Spring '12
 MrVinh

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