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Circle Problem

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Circle Problem

by gmat009 » Tue Oct 07, 2008 3:11 pm
In the xy-plane, the point (-2, -3) is the center of a circle. The point (-2, 1) lies inside the circle and the point (4, -3) lies outside the circle. If the radius r of the circle is an integer, then r =

A.6
B.5
C.4
D.3
E.2

OA is B
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by Gmatss » Tue Oct 07, 2008 4:40 pm
Not sure if my method is correct but, considering -2,-3 is the center and point 4,-3 is outside of the circle, and knowing that radius r is an integer, there are 5 spaces between -2,0 and 3,0 therefore raidus is 5.
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by gmat009 » Tue Oct 07, 2008 5:59 pm
Gmatss wrote:Not sure if my method is correct but, considering -2,-3 is the center and point 4,-3 is outside of the circle, and knowing that radius r is an integer, there are 5 spaces between -2,0 and 3,0 therefore raidus is 5.
But how do you know that (3,0) lies on the circle. It may be possible that 3,0 is also outside circle .
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by mental » Wed Oct 08, 2008 6:30 am
Centre of circle (-2, -3) and point (-2, 1): there are 4 spaces between them and lies inside circle
so radius>4


Centre of circle (-2, -3) and point (4, -3): there are 6 spaces between them and it lies outside circle
so radius < 6

4 < radius < 6

as radius is integer, radius = 5
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