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Given that xy > 0, which of the following must also be

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Magoosh GMAT Instructor
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Given that xy > 0, which of the following must also be [#permalink] New post 09 Jul 2013, 09:23
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E

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86% (01:50) correct 14% (00:36) wrong based on 42 sessions
Given that xy > 0, which of the following must also be greater than zero?

(A) x + y
(B) x^2 + y
(C) (x + y)^2
(D) x^2 - y^2 + 100
(E) (x - y)^2

For a discussion of plugging in numbers, as well as a full solution to this question, see:
http://magoosh.com/gmat/2013/how-to-plu ... questions/

Mike :-)
[Reveal] Spoiler: OA

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Mike McGarry
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Kudos [?]: 348 [0], given: 23

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Re: Given that xy > 0, which of the following must also be [#permalink] New post 09 Jul 2013, 09:49
mikemcgarry wrote:
Given that xy > 0, which of the following must also be greater than zero?

(A) x + y
(B) x^2 + y
(C) (x + y)^2
(D) x^2 - y^2 + 100
(E) (x - y)^2

For a discussion of plugging in numbers, as well as a full solution to this question, see:
http://magoosh.com/gmat/2013/how-to-plu ... questions/

Mike :-)


Actually if u just go through the options.. you'll notice that option C, is a perfect square.. which has to be greater than or equal to zero. Now looking back at the question, we know xy>0, which implies x and y are not equal to 0 and are of same sign. therefore x+y will be a non zero number and its square would be greater than 0.

Ans C it is.
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Re: Given that xy > 0, which of the following must also be   [#permalink] 09 Jul 2013, 09:49
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