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s_raizada Really wants to Beat The GMAT!
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Posted: Thu Jun 12, 2008 2:04 pm Post subject: If xy = 1 |
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| If xy = 1, what is the value of (2(x + Y)^2)/(2(x - Y)^2)??
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babachal Just gettin' started!
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Posted: Thu Jun 12, 2008 3:23 pm Post subject: |
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| Hey, can you give us full question?
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netigen GMAT Destroyer!
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Posted: Thu Jun 12, 2008 3:38 pm Post subject: |
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Question is what is the value of
2^(x + Y)^2)/2^(x - Y)^2
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egybs Really wants to Beat The GMAT!
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Posted: Thu Jun 12, 2008 4:02 pm Post subject: |
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ahhhh.. in that case it's easy!
2^(x+y)^2 / 2^(x-y)^2
2^((x+y)^2 - (x-y)^2)
2^(x^2 + 2xy + y^2 - x^2 + 2xy - y^2)
2^(4xy)
which as we know is equal to 2^4... so 16.
Last edited by egybs on Thu Jun 12, 2008 4:21 pm; edited 1 time in total |
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babachal Just gettin' started!
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Posted: Thu Jun 12, 2008 4:17 pm Post subject: |
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egybs, you did mistake in the last step
2^(x^2+2xy+y^2-x^2+2xy-y^2)+2^4xy=2^4=16
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egybs Really wants to Beat The GMAT!
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Posted: Thu Jun 12, 2008 4:20 pm Post subject: |
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| oops! yep. i did.
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s_raizada Really wants to Beat The GMAT!
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Posted: Fri Jun 13, 2008 1:36 am Post subject: |
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Hi guys,
question is not what you are calculating. See the screenshot of the question and it is form GMAT prep
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AleksandrM GMAT Destroyer!

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egybs Really wants to Beat The GMAT!
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Posted: Fri Jun 13, 2008 9:32 am Post subject: |
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| Can you give us the answer options...
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Ian Stewart GMAT Instructor

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Posted: Fri Jun 13, 2008 11:23 am Post subject: |
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| As has been posted elsewhere, there's a typo in the question itself. The solution posted above by netigen, with the x and y terms in the exponents, presented the question in the way it's supposed to be written.
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GMAT dreamer Just gettin' started!
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Posted: Tue Nov 18, 2008 12:16 pm Post subject: |
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We can make things simpler...
If xy=1; it tells that x=1 and y=1, right?
so, 2^(1+1)^2/2^(1-1)^2=
2^2^2/2^0^2=
2^4/2^0=
16/1= 16
Very simple we put numbers.
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cramya GMAT Titan
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Posted: Tue Nov 18, 2008 3:40 pm Post subject: |
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| Quote: | | If xy=1; it tells that x=1 and y=1, right? |
In general if xy=1 does not necessarily mean x=1 and y=1 unless there are other properties about x and y also given that confirms the fact that x=1 y=1
To quote a few:
x=-1 y=-1 xy=1
x=5 y=1/5 xy =1
x=-5 y=-1/5 xy=1
Unless it says x and y are positive integers and xy=1 we cannot assume
x=1 and y=1
Hope this helps!
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