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Which negative number x makes

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paddy41
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Which negative number x makes [#permalink] New post   11 Apr 2018, 06:30
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Question Stats:

74% (01:55) correct 26% (02:38) wrong based on 108 sessions
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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
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C
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chetan2u
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Re: Which negative number x makes [#permalink] New post   11 Apr 2018, 10:18
Expert Reply
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
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paddy41
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Re: Which negative number x makes [#permalink] 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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chetan2u
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Re: Which negative number x makes [#permalink] New post   13 Apr 2018, 10:26
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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
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Abhishek009
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Re: Which negative number x makes [#permalink] New post   18 Feb 2024, 08:27
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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

­ \(\frac{(7-x)}{3}=x^2+x\)­

Or, \(7 - x = 3x^2 + 3x\)

Or, \(3x^2 + 4x - 7 = 0\)­

Or, \(x = -\frac{7}{3}\) , \(1\), Answer must be (C)
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Re: Which negative number x makes [#permalink]
18 Feb 2024, 08:27
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