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Which negative number x makes

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Which negative number x makes [#permalink]

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New post 11 Apr 2018, 06:30
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Question Stats:

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Which negative number x makes \((7-x)/3\) equal to \(x^2+x\)

A.) -2/3
B.) -4/3
C.) -7/3
D.) -7/5
E.) -9/5
[Reveal] Spoiler: OA
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Re: Which negative number x makes [#permalink]

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New post 11 Apr 2018, 10:18
paddy41 wrote:
Which negative number x makes \((7-x)/3\) equal to \(x^2+x\)

A.) -2/3
B.) -4/3
C.) -7/3
D.) -7/5
E.) -9/5



\(\frac{7-x}{3}=x^2+x..............7-x=3x^2+3x...............3x^2+4x-7+0.........(x-1)(3x+7)=0\)

so x = 1 or \(\frac{-7}{3}\)

C..

Ofcourse SUBSTITUTION from choices is a good method
_________________

Absolute modulus :http://gmatclub.com/forum/absolute-modulus-a-better-understanding-210849.html#p1622372
Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html


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Posts: 31
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Re: Which negative number x makes [#permalink]

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New post 13 Apr 2018, 09:33
chetan2u wrote:
paddy41 wrote:
Which negative number x makes \((7-x)/3\) equal to \(x^2+x\)

A.) -2/3
B.) -4/3
C.) -7/3
D.) -7/5
E.) -9/5



\(\frac{7-x}{3}=x^2+x..............7-x=3x^2+3x...............3x^2+4x-7+0.........(x-1)(3x+7)=0\)

so x = 1 or \(\frac{-7}{3}\)

C..

Ofcourse SUBSTITUTION from choices is a good method


Dear chetan2u,

I somehow get stuck on the bold part. Could you briefly elaborate on this step?
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Re: Which negative number x makes [#permalink]

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New post 13 Apr 2018, 10:26
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Expert's post
paddy41 wrote:
chetan2u wrote:
paddy41 wrote:
Which negative number x makes \((7-x)/3\) equal to \(x^2+x\)

A.) -2/3
B.) -4/3
C.) -7/3
D.) -7/5
E.) -9/5



\(\frac{7-x}{3}=x^2+x..............7-x=3x^2+3x...............3x^2+4x-7+0.........(x-1)(3x+7)=0\)

so x = 1 or \(\frac{-7}{3}\)

C..

Ofcourse SUBSTITUTION from choices is a good method


Dear chetan2u,

I somehow get stuck on the bold part. Could you briefly elaborate on this step?



Hi...
\(7-x=3x^2+3x.........3x^2+4x-7=0.....3x^2+7x-3x-7=0.....x(3x+7)-1(3x+7)=0.....(x-1)(3x+7)=0\)..
So either x-1=0, that is x=1 OR 3x+7=0...x=-7/3 OR both x=1 and X=-7/3
But x is NEGATIVE , so x=-7/3

Hope it helps
_________________

Absolute modulus :http://gmatclub.com/forum/absolute-modulus-a-better-understanding-210849.html#p1622372
Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html


GMAT online Tutor

Re: Which negative number x makes   [#permalink] 13 Apr 2018, 10:26
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