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Re: Geometry DS [#permalink]
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rxs0005 wrote:
A circle with center (1, 0) and radius 2 lies in the coordinate plane . If point (x, y) lies on the circle is (x, y) in quadrant 2?

(1) | y | > 1
(2) | x | > 1


If you draw a circle, you can solve it quickly.

We can see that for the 2nd quadrant, the (x,y) coordinate must be between \((0,\sqrt{3})\) and \((-1,0)\).

As we can clearly see that, if the radius is 2 and center is at (1,0); the extreme value of x for 2nd quadrant will be 1-2=-1, where y will be 0.

We know the extreme value for x; i.e. -1

Let's find out the extreme value for y; y will be maximum when x=0;

We can find y where x=0 by Pythagoras theorem;

Distance between origin and the center is 1.
Distance between center and the intersection of circle and y-axis is 2(radius).

Thus, distance between origin and extreme value of y in 2nd quadrant = \(\sqrt{2^2-1^2}=\sqrt{3}\approx 1.73\)

Thus we know the extreme(maximum) value for both x and y in the 2nd quadrant.

\(x<=-1 & y<=1.73\)

1. |y| > 1

Thus y can be 1.2 or 1.8.
1.2<1.73
1.8>1.73

(x,y) may or may not be in the 2nd quadrant
Not Sufficient.

2. |x| > 1

As we know that the maximum value of x in 2nd quadrant is 1. (x,y) can't be in the 2nd quadrant because |x|>1.

Sufficient.

Ans: "B"
*****************

Please take a look at the image to get a visual clarification as well.
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quadrant_for_point_x_y_on_circle.PNG
quadrant_for_point_x_y_on_circle.PNG [ 9.87 KiB | Viewed 4396 times ]

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Re: Geometry DS [#permalink]
Thanks Fluke. Great explanation.
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Re: Geometry DS [#permalink]
Interesting! Consider this we move the center to origin then both statements are insufficient. But not now.

Posted from my mobile device
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Re: A circle with center (1, 0) and radius 2 lies in the [#permalink]
rxs0005 wrote:
A circle with center (1, 0) and radius 2 lies in the coordinate plane . If point (x, y) lies on the circle is (x, y) in quadrant 2?

(1) | y | > 1
(2) | x | > 1


Statement 1

Could be any quadrant actually

Statement 2

| x | > 1 means either x>1 or x<-1

Since circle has radius 2 and centered at (1,0) then x cannot be less than -1.

Therefore, x>1

So it CANNOT be on the second quadrant

Hence, answer is B only

Hope it helps!
Cheers!
J :)
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Re: A circle with center (1, 0) and radius 2 lies in the [#permalink]
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Re: A circle with center (1, 0) and radius 2 lies in the [#permalink]
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