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Which of the following equations is not equivalent to 36y^2 + 9 = x^2?

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Math Expert
Joined: 02 Sep 2009
Posts: 46250
Which of the following equations is not equivalent to 36y^2 + 9 = x^2? [#permalink]

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17 Oct 2017, 23:34
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Difficulty:

15% (low)

Question Stats:

87% (00:45) correct 13% (00:32) wrong based on 60 sessions

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Which of the following equations is not equivalent to $$36y^2 + 9 = x^2$$?

(A) $$36y^2 = x^2 - 9$$

(B) $$36y^2 = (x - 3)(x + 3)$$

(C) $$108y^2 + 27 = 3x^2$$

(D) $$y^2 = \frac{x^2 - 9}{36}$$

(E) $$6y = x - 3$$

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Re: Which of the following equations is not equivalent to 36y^2 + 9 = x^2? [#permalink]

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18 Oct 2017, 02:13
E because squaring both sides won't give the desired equation.
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Joined: 22 May 2017
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GMAT 2: 580 Q43 V27
Re: Which of the following equations is not equivalent to 36y^2 + 9 = x^2? [#permalink]

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22 Oct 2017, 12:00
Bunuel wrote:
Which of the following equations is not equivalent to $$36y^2 + 9 = x^2$$?

(A) $$36y^2 = x^2 - 9$$

(B) $$36y^2 = (x - 3)(x + 3)$$

(C) $$108y^2 + 27 = 3x^2$$

(D) $$y^2 = \frac{x^2 - 9}{36}$$

(E) $$6y = x - 3$$

Just rearrange other equation to equation mention in the question. You will get the answer. I must say worse question on GMATclub.

E does not belong to the group.
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Joined: 09 Aug 2017
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Location: United States
Concentration: Technology
GMAT 1: 640 Q44 V33
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Re: Which of the following equations is not equivalent to 36y^2 + 9 = x^2? [#permalink]

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23 Oct 2017, 17:55
I went with E and I tried to go so slow so as not to make a simple mistake.

E gave me some pause, because the square root of 36y^2 is 6y. However, the square root of x^2-9 isn't x-3. So that's what sealed it for me.

I wasted time on the earlier answers and just needed to stay calm, focus and not make stupid mistake.
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I'd love to hear any feedback or ways to improve my problem solving. I make a lot of silly mistakes. If you've had luck improving on stupid mistakes, I'd love to hear how you did it.

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Re: Which of the following equations is not equivalent to 36y^2 + 9 = x^2? [#permalink]

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23 Oct 2017, 18:01
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IMO Option E
On squaring both sides won't give the equation.
Please give me kudos. I need them badly to unlock gmatclub tests
Re: Which of the following equations is not equivalent to 36y^2 + 9 = x^2?   [#permalink] 23 Oct 2017, 18:01
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