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by GmatMathPro » Mon Dec 19, 2011 3:33 pm
Square both sides of the equation to get x^2=4xy-4y^2.

x^2-4xy+4y^2=0 (bring everything to one side)

(x-2y)^2=0 (factor)

x-2y=0 (set factors equal to zero)

x=2y (solve)


Ans: A
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by GMATGuruNY » Mon Dec 19, 2011 3:40 pm
karthikpandian19 wrote:XY problem refer IMAGE
Image
Let y=1.

Then:
x = √(4x(1) - 4*1²)
x = √(4x - 4)
x² = 4x-4
x²-4x+4 = 0
(x-2)(x-2) = 0
x=2. This is our target.

Now we plug y=1 into the answers to see which yield our target of 2.
Only answer choice A works:
2y = 2(1) = 2.

The correct answer is A.
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by karthikpandian19 » Wed Dec 28, 2011 9:54 pm
OA is A
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