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# If xy=1, ...

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Senior Manager
Joined: 28 Feb 2007
Posts: 293

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03 Sep 2008, 14:16
Here is the question that made me crazy and that wiped almost 5 min out.
Could u plz, share ur approach to solve it as fast as possible.

If xy=1 then what is the value of [2(x+y)^2] / [2(x-y)^2]

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

source GmatPrep.

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Manager
Joined: 09 Jul 2007
Posts: 235

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03 Sep 2008, 14:29
Unless I am reading something wrong , I do not think we can anser this question with the information provided :

xy=1 then what is the value of [2(x+y)^2] / [2(x-y)^2]

lets consider 2 sets of values for x and Y (2,1/2) and (3,1/3)

the value for the 1st expression will be = [2(x+y)^2] / [2(x-y)^2] =[ 1.5^2/.5^2]=9

the valuse for the 2nd set will be = [ 1.33^2 / .67^2 ] = 4

so the valuse can be anything unless some more information is given.. can you please check that you have written the expression correctly [2(x+y)^2] / [2(x-y)^2]
Senior Manager
Joined: 28 Feb 2007
Posts: 293

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03 Sep 2008, 14:32
I wrote the question as it appeared.
When I saw this question first thing that popped up in my mind was THIS QUESTION IS ABNORMAL.
Indeed, we cannot solve it with the given structure.
Director
Joined: 12 Jul 2008
Posts: 511
Schools: Wharton

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03 Sep 2008, 15:35
UMB wrote:
Here is the question that made me crazy and that wiped almost 5 min out.
Could u plz, share ur approach to solve it as fast as possible.

If xy=1 then what is the value of [2(x+y)^2] / [2(x-y)^2]

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

source GmatPrep.

I think it's supposed to say 2^((x+y)^2)/2^((x-y)^2)
VP
Joined: 05 Jul 2008
Posts: 1333

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03 Sep 2008, 17:02
The Q as it is written here seems weird and unsolvable.

Why dont you attach the screen shot? That takes away the confusion and every one can chime in.
VP
Joined: 17 Jun 2008
Posts: 1477

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04 Sep 2008, 00:36
I have seen this question with the format what zoinnk has mentioned. However, if the question is as mentioned originally, and if it asks "what could be the value", I will approach it as below.

2[x+y]^2/2[x-y]^2 = [(x-y)^2 + 4xy]/(x-y)^2 = 1 + 4/(x-y)^2 = 1 + 4x^2/(x^2-1)^2.

And, for any value of x, none of the answer choices will be the result.
Current Student
Joined: 11 May 2008
Posts: 551

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04 Sep 2008, 02:28
If xy=1 then what is the value of [2(x+y)^2] / [2(x-y)^2]

it should be 2^(x+y)^2/2^(x-y)^2.
we get ans as 4.

--== Message from GMAT Club Team ==--

This is not a quality discussion. It has been retired.

If you would like to discuss this question please re-post it in the respective forum. Thank you!

To review the GMAT Club's Forums Posting Guidelines, please follow these links: Quantitative | Verbal Please note - we may remove posts that do not follow our posting guidelines. Thank you.
Re: If xy=1, ...   [#permalink] 04 Sep 2008, 02:28
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# If xy=1, ...

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