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If x^2 - 9 = 0 and x < 0, which of the following must be equ

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run4run
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If x^2 - 9 = 0 and x < 0, which of the following must be equ [#permalink] New post   Updated on: 08 Feb 2014, 02:49
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67% (01:33) correct 33% (01:36) wrong based on 58 sessions
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If x^2 - 9 = 0 and x < 0, which of the following must be equal to 0 ?

(A) x^2 - 9x
(B) x^2 - 9x + 20
(C) x^2 - 2x + 3
(D) x^2 + 2x - 3
(E) x^2 + 5x + 6

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Answer: D
First, find the possible values of x in the given equation. x^2 - 9 = (x + 3)(x - 3), so since that expression is set equal to zero, x could be 3 or -3. Since we're told that x < 0, x must be -3.

There are two ways to identify the correct choice. You can plug -3 into each of the five choices, or you can factor each of the five choices, looking for one that includes the term (x + 3). Try the latter:

(A) = x(x - 9)
(B) = (x - 5)(x - 4)
(C) = (x - 3)(x + 1)
(D) = (x + 3)(x - 1)
(E) = (x + 5)(x + 1)

(D) is correct.


That all being said can't the answer be E as well? And isn't his factoring of E wrong? Thanks

Run



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Official Answer
D

Originally posted by run4run on 10 May 2010, 11:20.
Last edited by Bunuel on 08 Feb 2014, 02:49, edited 1 time in total.
Renamed the topic, edited the question and added the OA.
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lagomez
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Re: If x^2 - 9 = 0 and x < 0, which of the following must be equ [#permalink] New post   10 May 2010, 11:55
run4run wrote:
If x^2 - 9 = 0 and x < 0, which of the following must be equal to 0 ?
(A) x^2 - 9x
(B) x^2 - 9x + 20
(C) x^2 - 2x + 3
(D) x^2 + 2x - 3
(E) x^2 + 5x + 6
Show Spoiler
Answer: D
First, find the possible values of x in the given equation. x^2 - 9 = (x + 3)(x - 3), so since that expression is set equal to zero, x could be 3 or -3. Since we're told that x < 0, x must be -3.

There are two ways to identify the correct choice. You can plug -3 into each of the five choices, or you can factor each of the five choices, looking for one that includes the term (x + 3). Try the latter:

(A) = x(x - 9)
(B) = (x - 5)(x - 4)
(C) = (x - 3)(x + 1)
(D) = (x + 3)(x - 1)
(E) = (x + 5)(x + 1)

(D) is correct.




That all being said can't the answer be E as well? And isn't his factoring of E wrong? Thanks

Run


Yes, I have caught errors myself in his questions. I usually just end up sending him an email and he responds that a. he has corrected it or b. there is an oversight. In this case, I think it's the former rather than the latter.
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lnarayanan
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Re: If x^2 - 9 = 0 and x < 0, which of the following must be equ [#permalink] New post   10 May 2010, 12:00
I agree to.. Ans E also satisfies the condition
x^2-9 = 0
x= +3 or x = -3
if we substitute x= -3 in the equation x^2 +5x+6 = 9-15+6 = 0
E is also the answer
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Silvers
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Re: If x^2 - 9 = 0 and x < 0, which of the following must be equ [#permalink] New post   10 May 2010, 12:21
Where did u get this question from?

cause like everyone says the answer can be E too.
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run4run
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Re: If x^2 - 9 = 0 and x < 0, which of the following must be equ [#permalink] New post   10 May 2010, 12:44
I got this from Jeff Sackman's question of the day. It's an email you can sign up for where he sends you a question a day pretty much like the Gmatclub question of the day
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agnok
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Re: If x^2 - 9 = 0 and x < 0, which of the following must be equ [#permalink] New post   10 May 2010, 14:53
E too it is... this is an error... either D or E... Thanks for the Jeff smacks info... does anyone have the Jeff Sackmann material?
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dixitraghav
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Re: If x^2 - 9 = 0 and x < 0, which of the following must be equ [#permalink] New post   18 May 2010, 10:09
this question contains multiple answers



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Hi there,
This topic has been closed and archived due to inactivity or violation of community quality standards. No more replies are possible here.
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Still interested in this question? Check out the "Best Topics" block above for a better discussion on this exact question, as well as several more related questions.
Thank you for understanding, and happy exploring!
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Re: If x^2 - 9 = 0 and x < 0, which of the following must be equ [#permalink]
18 May 2010, 10:09
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