jitendra wrote:
Circle C is in the xy-plane, what is the area of the circle?
(1) Points (-2, 0) and (0,2) lie on the circle.
(2) The radius of the circle is equal to or less than 2^(1/2).
area=\pi{r^2}, so we should find the value of radius.
It would be better if you visualize this problem.
(1) Points (-2, 0) and (0,2) lie on the circle --> two points DO NOT define a circle (three points does), hence we can have numerous circles containing these two points, thus we can not find single numerical value of radius. Not sufficient.
Side note: if you put points (-2, 0) and (0,2) on XY-plane you can see that center of the circle must be on the line
y=-x (the center of the circle must be equidistant from two pints given).
(2) The radius of the circle is equal to or less than
\sqrt{2} -->
r\leq{\sqrt{2}}. Clearly insufficient.
(1)+(2) The distance between the 2 points given is
d=\sqrt{2^2+2^2}=2\sqrt{2}, so it's min length of diameter of the circle passing these points (diameter of a circle passing 2 points can not be less than the distance between these 2 points), thus half of
2\sqrt{2} is min length of the radius of the circle -->
r\geq{\sqrt{2}} but as from (2)
r\leq{\sqrt{2}} then
r=\sqrt{2} -->
area=\pi{r^2}=2\pi. Sufficient.
Answer: C.
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44% (02:58) correct
