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DS

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Source: — Data Sufficiency |
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Re: DS

by sudhir3127 » Thu Aug 28, 2008 8:13 am
gmattester wrote:If a^2 - b^2=0, does a=0
1) ab=0
2)b=-b
IMO C
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Re: DS

by gmattester » Thu Aug 28, 2008 8:30 am
sudhir3127 wrote:
gmattester wrote:If a^2 - b^2=0, does a=0
1) ab=0
2)b=-b
IMO C
Even I got answer C but somewhere I read answer A, so got confused
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by rishi235 » Thu Aug 28, 2008 9:04 am
I'm getting A

Heres wat I did:
a^2 = b^2
=> a = +/-b

From stmt 1)
ab=0
=> a=0 or b=0...
=> So irrespective of the sign of b, a = b = 0...SUFFICIENT

Please tell me where I'm going wrong...
Thanks
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by anshul265 » Thu Aug 28, 2008 9:25 am
from the question we get

(a+b) (a-b) =0
either (a+b)=0
or (a-b) =0

from statement 1
ab=0
either a=0 , or b=0
insufficient

from statment 2
b =-b
b+b=0
2b =0
b =0

Now if b=0, then a has to be 0
sufficient

IMO B
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by gmattester » Thu Aug 28, 2008 11:19 am
So many different answers.
Totally confused.........
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Re: DS

by Ian Stewart » Thu Aug 28, 2008 2:25 pm
gmattester wrote:If a^2 - b^2=0, does a=0
1) ab=0
2)b=-b
I think in some of the solutions above, people are not using the information provided in the question. We know, to begin with, that

a^2 - b^2 = 0

There are a few ways to rewrite this, but no matter how you do, you should find that

|a| = |b|

That is, if a is zero, then b must be zero, and vice versa.

From 1), we know either a is zero or b is zero, so the other must be zero as well. Sufficient.

Statement 2 could only be true if b is zero, so a must be zero as well. Sufficient.

D.
For online GMAT math tutoring, or to buy my higher-level Quant books and problem sets, contact me at ianstewartgmat at gmail.com

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by gmattester » Thu Aug 28, 2008 3:50 pm
Thanks Ian........
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by niraj_a » Thu Aug 28, 2008 5:47 pm
WOWOWOW
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