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by anshulseth » Tue May 12, 2009 10:06 am
What is the value of x^2 – 1 ?

1. The value of x^2 – 5x is –6.
2. The value of (x^2-1)/(x+1) is 1.

Regular DS options.

Explain the working plz. Don't just guess.
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by gauravgundal » Tue May 12, 2009 10:19 am
I would go for C

STM -1

x^2 -5x=-6
x^2 -5x+6=0
x=3 and x=2
Insufficient

STM-2
x^2 -1=x+1
x^2 -x-2=0
x=2 and x =-1
Insufficient

Combining both i can say x=2
x^2-1=3

Please let me know if i am wrong.
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by HumbleMe » Tue May 12, 2009 10:22 am
1. x^2-5x = 6 -> x=2 or x=3 -> x^2-1 = 3 or 8

2. x^2-1/x+1 = (x-1)(x+1)/(x+1) = x-1 = 1 -> x = 2

Only 2 is sufficient... Hence B
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by gauravgundal » Tue May 12, 2009 10:28 am
My Mistake
humble u are right
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by anshulseth » Tue May 12, 2009 6:52 pm
@HumbleMe

My question to you is:
Do you know if X is not equal to -1.
Then, how can u cancel X+1 in the 2) option.
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by 2010gmat » Tue May 12, 2009 11:30 pm
if x = -1 then (x^2-1)/(x+1) = 1 is not possible....
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by anshulseth » Tue May 12, 2009 11:47 pm
Got it.
Thanks 2010gmat
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