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# if XY=1, then what is (2*(x+y)^2) / (2*(x-y)^2) a) 2 b) 4 c)

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Manager
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if XY=1, then what is (2*(x+y)^2) / (2*(x-y)^2) a) 2 b) 4 c) [#permalink]

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10 Nov 2005, 17:10
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

if XY=1, then what is (2*(x+y)^2) / (2*(x-y)^2)

a) 2
b) 4
c) 8
d) 16
e) 32

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10 Nov 2005, 17:38
hey conocieur, is this question complete?

just a thought cause I am not able to see how to solve this.
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10 Nov 2005, 17:44
i took a sample test from gmatprep today, and this was one of the questions, i couldn't solve it even using backsolving.

However, I believe it can be solved with the information given

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SVP
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10 Nov 2005, 18:47
No Solution can be reached.

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10 Nov 2005, 18:47
Is it mentioned that X or Y is an integer?

If it is then you can solve this by some estimation:

XY = 1 => Y=1/X

Substituting you get: ((X^2 + 1)/(X^2 - 1))^2
If x is an integer than the highest value for (X^2 + 1)/(X^2 - 1) = let's say A, is when x = 2

x = 2, A = 5/3
x = 3, A = 5/4
x = 4, A = 17/15 and so on

So the maximum value of A^2 can be 25/9 = 2.7 something

therefore, i would go with A

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10 Nov 2005, 19:48
Hmmm...I simplified it down to (y^2+1)/(y^2-1) but cannot solve with the info given

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11 Nov 2005, 06:49
Is * mult and ^ an exponent?

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11 Nov 2005, 08:10
rianah100 wrote:
Is * mult and ^ an exponent?

yes * is mult and ^ exp,

as I said before I couldn't solve this problem from gmatprep, but I remember other DS problem asking if (x+y)^2 / (x-y)^2 can be solved when
xy=3, and the answer was yes, so my problem can be solved as well

thanks

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11 Nov 2005, 08:18
If D is the OA then
i think the question is worded wrong; its got to be

(2^(x+y)^2) / (2^(x-y)^2)

ans is 2^(4xy)=16
D

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11 Nov 2005, 08:26
I don't think it can be solved.

I think the question should have been
if XY=1, then what is (2*(x+y)^2) - (2*(x-y)^2)

only then you can solve it by 2 * 4xy = 8

and C is the answer.

other wise in can be anything.
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hey ya......

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Director
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11 Nov 2005, 10:01
yup couldn't solve it ....there is somthing wrong with question statement....

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11 Nov 2005, 10:39
I remember getting a similar problem....dont know how to solve it...

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11 Nov 2005, 10:51
conocieur, can you attach image of the problem..maybe there is something hidden somewhere
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12 Nov 2005, 00:33
I also remember this is one question I faced in Powerprep software. I couldn't solve it. There can be multiple answers for this question, with the information given.

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12 Nov 2005, 00:33
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# if XY=1, then what is (2*(x+y)^2) / (2*(x-y)^2) a) 2 b) 4 c)

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