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Fraction DS Problem, need some help!

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cgjkim1
 Post subject: Fraction DS Problem, need some help!
 Post Posted: Thu Nov 17, 2011 12:42 am 
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If a^2-b^2=0, does a=0?
1) ab=0
2) b=-b

The answer sheet said it is D. But I can't figure out why it is D.
Someone please help me. Thanks for your knowledge.
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surya.anem
 Post subject: Re: Fraction DS Problem, need some help!
 Post Posted: Thu Nov 17, 2011 2:24 am 
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Hi,

Not sure if my explanation is correct. Infact if i had been faced this problem i wouldnt have definitely tried this way. But tried to backtrace based on your answer.

a^2 - b^2 = 0
so a^2 = b^2 -> a = b or - b

Actually the above will happen only if a and b are both zeroes.

Infact without any clues may be we can guess that.

1)ab=0, we know that a=b or -b, substituting we get a = 0
2) b=-b only for 0. Once again substituting above..we get a=0.


Thanks
Surya
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tim
 Post subject: Re: Fraction DS Problem, need some help!
 Post Posted: Wed Nov 23, 2011 2:12 pm 
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ManhattanGMAT Staff


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Location: Southwest Airlines, seat 21C
Thanks Surya. Not sure how this got the title of ”Fraction DS Problem”, but oh well..

_________________
Tim Sanders
Manhattan GMAT Instructor
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