rxs0005
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"
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Please take a look at the image to get a visual clarification as well.
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