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arjtryarjtry
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a^2 - b^2 = b^2 - c^2 . Is a = |b| ? 1) b = |c| 2) b = |a| * 29 Aug 2008, 00:48
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a^2 - b^2 = b^2 - c^2 . Is a = |b| ?

1) b = |c|
2) b = |a|


* Statement (1) ALONE is sufficient, but Statement (2) ALONE is not sufficient
* Statement (2) ALONE is sufficient, but Statement (1) ALONE is not sufficient
* BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient
* EACH statement ALONE is sufficient
* Statements (1) and (2) TOGETHER are NOT sufficient



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a^2 - b^2 = b^2 - c^2 . Is a = |b| ? 1) b = |c| 2) b = |a| * 29 Aug 2008, 00:59
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(a+b)*(a-b) = (b+c)*(b-c)


From ( i ) b = c or b = -c

If b = c, then a = b or a = -b, which implies a = |b|

If b = -c, then a = b or a = -b, which implies a = |b|

Thus ( i ) is sufficient

From ( ii ) b = a or b = -a

also shows that a = |b|

Thus ( ii ) is sufficient


Thus answer should be "D"
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a^2 - b^2 = b^2 - c^2 . Is a = |b| ? 1) b = |c| 2) b = |a| * 29 Aug 2008, 02:35
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arjtryarjtry
a^2 - b^2 = b^2 - c^2 . Is a = |b| ?

1) b = |c|
2) b = |a|


* Statement (1) ALONE is sufficient, but Statement (2) ALONE is not sufficient
* Statement (2) ALONE is sufficient, but Statement (1) ALONE is not sufficient
* BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient
* EACH statement ALONE is sufficient
* Statements (1) and (2) TOGETHER are NOT sufficient
Show more

Guessing E

not sure if I interpret what the question is asking correctly.

The question is asking if a is positive.

rearrange the stem to

a^2 + c^2 = b^2 + b^2

statement 1: b^2 = c^2 leads to a^2 = b^2
a could be positive or negative
insuff

statement 2: a^2 = b^2, it is the same as statement 1, so insuff

together, 2 statements are the same
insuff
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x2suresh
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a^2 - b^2 = b^2 - c^2 . Is a = |b| ? 1) b = |c| 2) b = |a| * 29 Aug 2008, 07:42
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arjtryarjtry
a^2 - b^2 = b^2 - c^2 . Is a = |b| ?

1) b = |c|
2) b = |a|


* Statement (1) ALONE is sufficient, but Statement (2) ALONE is not sufficient
* Statement (2) ALONE is sufficient, but Statement (1) ALONE is not sufficient
* BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient
* EACH statement ALONE is sufficient
* Statements (1) and (2) TOGETHER are NOT sufficient
Show more

1) b = |c|
a^2 - b^2 =0 a=b or a=-b ( b is positive and a can be -ve or +ve)
Is a = |b| ? Yes or No
multiple answers
not suffcieint
2) b = |a| b= a or b=-a (a is -ve and b is positive)
Is a = |b| ? Yes or No
insuffcient

combine.
not suffcient
E
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a^2 - b^2 = b^2 - c^2 . Is a = |b| ? 1) b = |c| 2) b = |a| * 29 Aug 2008, 08:41
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Rephrase the question as:

If |a| = |b| = |c|, is a positive?

1) b = |c|, thus b is positive. Nothing about a. INSUFF.
2) b = |a|, thus b is positive. Again, nothing about a. INSUFF
Clearly 1+2 taken together are also INSUFF.
Anwer: E for me.
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a^2 - b^2 = b^2 - c^2 . Is a = |b| ? 1) b = |c| 2) b = |a| * 30 Aug 2008, 04:34
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arjtryarjtry
a^2 - b^2 = b^2 - c^2 . Is a = |b| ?

1) b = |c|
2) b = |a|


* Statement (1) ALONE is sufficient, but Statement (2) ALONE is not sufficient
* Statement (2) ALONE is sufficient, but Statement (1) ALONE is not sufficient
* BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient
* EACH statement ALONE is sufficient
* Statements (1) and (2) TOGETHER are NOT sufficient
Show more


Interesting problem. If I take a look at this problem more abstractly, the question is asking whether a is positive or zero.

(1) b is zero or positive. So, if you take the absolute value of b from this restriction, a will be either positive or zero. True

(2) we don't know the actual sign of a, however, because b is either positive or zero, the absolute value of that will also be positive or a zero, so suff.

Damn, I really hate these kind of problems, but I believe that it should be D?

by the way, what is the abstract meaning behind \(a^2-b^2=b^2-c^2\)? This expression must be telling us something, but I can't seem to figure out what it is. For example, if we would have the expresion \(|x+y|<|x|+|y|\), then you would know instantly that the signs for x and y are opposite from each other. So what is the expression from this problem trying to tell us without doing any math. There must be a message behind this expression.
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a^2 - b^2 = b^2 - c^2 . Is a = |b| ? 1) b = |c| 2) b = |a| * 30 Aug 2008, 14:08
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I will go with C.

The question is really asking whether square of a is the same as that of b.

From stmt 1, if b = |C| then b^2 = c^2 and hence a^2 - b^2 = 0 i.e. a^2 = b^2. Hence, sufficient.

Stmt2 is the repeat of question itself....hence sufficient.
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a^2 - b^2 = b^2 - c^2 . Is a = |b| ? 1) b = |c| 2) b = |a| * 30 Aug 2008, 14:32
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scthakur
I will go with C.

The question is really asking whether square of a is the same as that of b.

From stmt 1, if b = |C| then b^2 = c^2 and hence a^2 - b^2 = 0 i.e. a^2 = b^2. Hence, sufficient.

Stmt2 is the repeat of question itself....hence sufficient.
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you said that each statement is suff. but you choose C as your answer?
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a^2 - b^2 = b^2 - c^2 . Is a = |b| ? 1) b = |c| 2) b = |a| * 31 Aug 2008, 05:11
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so what's the OA to this question?
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a^2 - b^2 = b^2 - c^2 . Is a = |b| ? 1) b = |c| 2) b = |a| * 31 Aug 2008, 05:25
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IMO E.

a^2 - b^2 = b^2 - c^2 . Is a = |b| ?

1) b = |c|

If we fit this in the above equation, then a^2 - b^2 =0 => a= + or - b

So A alone not sufficient ( as a =|b| menas a is +ve )

2) b = |a|

b is + ve . but a can be +ve or -ve. So reverse is not true.


Even after combining, a =+ or - b and b = +ve which does not indicate if a is + ve or not.
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a^2 - b^2 = b^2 - c^2 . Is a = |b| ? 1) b = |c| 2) b = |a| * 31 Aug 2008, 06:07
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arjtryarjtry, what's the OA? almost all of us have come up with a different answer. I need to know the OA so that i can sleep well tonight. hehe...
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a^2 - b^2 = b^2 - c^2 . Is a = |b| ? 1) b = |c| 2) b = |a| * 31 Aug 2008, 06:45
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IMO E)

a = |b| statement shows that a is always +ve but a can be -ve or + ve from both statements
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a^2 - b^2 = b^2 - c^2 . Is a = |b| ? 1) b = |c| 2) b = |a| * 31 Aug 2008, 08:52
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ok guys, I managed to find the OA to this question. The OA is E.



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