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# ds: abs value

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Senior Manager
Joined: 17 May 2005
Posts: 272
Location: Auckland, New Zealand
Followers: 1

Kudos [?]: 5 [0], given: 0

HongHu wrote:
Don't be fooled by the seemly complexity of this question.

The question asks if a=|b|. With absolute value questions your first relection should be "do we know it's sign?" |b| is non negative. If we aren't able to determine if a is non negative then we can't determine if a=|b|.

Now look at the stem: a^2-b^2=b^2-c^2
and the two choices:
b=|c| and b=|a|
All we know is b is non negative. Do we know anything about a's sign? No!

Honghu, I am not sure if your approach to this particular question is right, because the question is really asking us whether a = b irrespective of their signs, so this can be deduced to is a^2 = b^2.

the question isn't asking whether a=b irrespective of their signs...
it asks for whether a = |b|
which would mean that a can't be negative
if signs didn't matter the question would be is |a|=|b|
Director
Joined: 03 Nov 2004
Posts: 868
Followers: 1

Kudos [?]: 19 [0], given: 0

cloudz9 wrote:
which would mean that a can't be negative

cloudz9, Thanks for correcting my oversight.
Senior Manager
Joined: 21 Mar 2004
Posts: 444
Location: Cary,NC
Followers: 2

Kudos [?]: 20 [0], given: 0

another vote for E.

A. simplifying we get |a| = |b| ,this is not same as a=|b|
so this is insufficient

B. simplifying we get |b| = |c| and given b=|a|
we still are not sure about a so this is insufficient too.

C. still doesnt help
_________________

ash
________________________
I'm crossing the bridge.........

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