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# What is the value of x^2 + y^2? 1) x^2 + y^2 = 2xy + 1 2)

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Intern
Joined: 03 Feb 2010
Posts: 29
Schools: HBS
What is the value of x^2 + y^2? 1) x^2 + y^2 = 2xy + 1 2) [#permalink]

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24 Jul 2010, 08:50
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Difficulty:

35% (medium)

Question Stats:

75% (02:23) correct 25% (00:44) wrong based on 8 sessions

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What is the value of x^2 + y^2?
1) x^2 + y^2 = 2xy + 1
2) x^2 + y^2 = 4 - 2xy

My question is why can't the answer be C?
2 (x^2 + y^2 ) = 5
Therefore x^2 + y^2 = 5/2

Am I am missing something obvious here?
[Reveal] Spoiler: OA
Intern
Joined: 10 Apr 2008
Posts: 24
Re: DS from Sackmann's Challenge Algrebra Set [#permalink]

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24 Jul 2010, 10:40
I also got C using the same method as youven.

S1 can be simplified to say (x-y)^2 = 1. That means (x-y) can be -1 or +1.
Similarly, S2 can be simplified to say (x-y)^2 = 4. That means (x+y) can be -2 or +2.

Solving for x and y, I get x=3/2 or x=-3/2 and y=1/2 or y=-1/2. For all the possible values of x and y, x^2 + y^2 will only be one value.

Can you someone help identify what I am doing wrong?

Thanks
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Re: DS from Sackmann's Challenge Algrebra Set [#permalink]

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24 Jul 2010, 11:32
seems to be C only.

Please check the question again,and if possible post OE
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Intern
Joined: 03 Feb 2010
Posts: 29
Schools: HBS
Re: DS from Sackmann's Challenge Algrebra Set [#permalink]

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24 Jul 2010, 12:00
Manager
Joined: 03 Jun 2010
Posts: 181
Location: United States (MI)
Concentration: Marketing, General Management
Re: DS from Sackmann's Challenge Algrebra Set [#permalink]

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26 Jul 2010, 04:39
(E)
Can't uderstand how you got (C)-)
Intern
Joined: 03 Feb 2010
Posts: 29
Schools: HBS
Re: DS from Sackmann's Challenge Algrebra Set [#permalink]

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26 Jul 2010, 07:38
ulm wrote:
(E)
Can't uderstand how you got (C)-)

well just read my first post and you will see how i came up with C
Manager
Joined: 18 Oct 2008
Posts: 191
Re: DS from Sackmann's Challenge Algrebra Set [#permalink]

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26 Jul 2010, 10:07
I am getting C again..

will be good to hear from Sackmann!
Re: DS from Sackmann's Challenge Algrebra Set   [#permalink] 26 Jul 2010, 10:07
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