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gmattester
- Master | Next Rank: 500 Posts
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IMO Cgmattester wrote:If a^2 - b^2=0, does a=0
1) ab=0
2)b=-b
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Source: Beat The GMAT — Data Sufficiency |
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
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
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
(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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Ian Stewart
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I think in some of the solutions above, people are not using the information provided in the question. We know, to begin with, thatgmattester wrote:If a^2 - b^2=0, does a=0
1) ab=0
2)b=-b
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.
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