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# sovlve in terms of y.

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Senior Manager
Joined: 17 Mar 2009
Posts: 278
sovlve in terms of y. [#permalink]

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09 Aug 2009, 09:00
00:00

Difficulty:

(N/A)

Question Stats:

60% (01:42) correct 40% (03:18) wrong based on 5 sessions

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If x and y are non-zero integers, and 9x^4 – 4y^4 = 3x^2 + 2y^2, which of the following could be the value of x2 in terms of y?
A) -4y^2/3

B) -2y^2

C) (2y^2+1)/3

D) 2y^2

E) 6y^2/3

OA:
[Reveal] Spoiler:
C

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

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Last edited by crejoc on 09 Aug 2009, 11:58, edited 1 time in total.
Manager
Joined: 18 Jul 2009
Posts: 166
Location: India
Schools: South Asian B-schools
Re: sovlve in terms of y. [#permalink]

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09 Aug 2009, 11:31
1
KUDOS
9x^4 – 4y^4 = 3x^2 + 2y^2

(3x^2)^2 – (2y^2)^2 = (3x^2 + 2y^2)

(3x^2 + 2y^2)(3x^2 - 2y^2)=(3x^2 + 2y^2)...this means (3x^2 - 2y^2)= 1

hence x^2 = (2y^2+1)/3...OA C
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Bhushan S.
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Manager
Joined: 28 Jul 2009
Posts: 119
Location: India
Schools: NUS, NTU, SMU, AGSM, Melbourne School of Business
Re: sovlve in terms of y. [#permalink]

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10 Aug 2009, 01:18
Agree with Bhushan! Answer would be C.
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Director
Joined: 01 Apr 2008
Posts: 846
Name: Ronak Amin
Schools: IIM Lucknow (IPMX) - Class of 2014
Re: sovlve in terms of y. [#permalink]

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10 Aug 2009, 02:34
bhushan252 wrote:
9x^4 – 4y^4 = 3x^2 + 2y^2

(3x^2)^2 – (2y^2)^2 = (3x^2 + 2y^2)

(3x^2 + 2y^2)(3x^2 - 2y^2)=(3x^2 + 2y^2)...this means (3x^2 - 2y^2)= 1

hence x^2 = (2y^2+1)/3...OA C

Perfect ! Only one thing to note here, we can reduce to the expression marked in RED only if we are sure that the expression (3x^2 + 2y^2) is non-zero, which is evident from the fact that x and y are non-zero

--== 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: sovlve in terms of y.   [#permalink] 10 Aug 2009, 02:34
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