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if X ____ = X, Which of the following must be true for all

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if X ____ = X, Which of the following must be true for all [#permalink] New post 26 Aug 2008, 09:41
if
X
____ = X, Which of the following must be true for all X?
|X|

x>1
x (BELONGS TO) (-1,0)U(1,infinity)
|x|<1
|x|=1
|x|^2>1

i could not understand the meaning.. pls explain

OA is B.
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Re: dont understand meaning... [#permalink] New post 26 Aug 2008, 09:48
arjtryarjtry wrote:
if
X
____ = X, Which of the following must be true for all X?
|X|

x>1
x (BELONGS TO) (-1,0)U(1,infinity)
|x|<1
|x|=1
|x|^2>1

i could not understand the meaning.. pls explain

OA is B.


Are you sure you typed the question properly ?
If x/|x| = x then then it is satisfied by only two values of x. 1 and -1. I would think D is the answer.

Last edited by bhushangiri on 26 Aug 2008, 10:11, edited 1 time in total.
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Re: dont understand meaning... [#permalink] New post 26 Aug 2008, 09:55
its a club question...
the q's right.
its X/|X|
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Re: dont understand meaning... [#permalink] New post 26 Aug 2008, 10:00
The U means UNION.

If you have 2 groups, then this is saying that x belongs to group that is shared by both, meaning where the groups are the same, also referred to as UNION, like in Venn Diagrams.

With b), You have the group of -1,0, and then 1,infinity.

It appears that B is saying that the only values that satisfy the question are 1, -1, 0, and infinity. It is a confusing question, but you can also arrive at the answer of B by process of elimination.

arjtryarjtry wrote:
if
X
____ = X, Which of the following must be true for all X?
|X|

a) x>1 Incorrect. MUST BE TRUE, but is x = 2, then 2/|2| = 1, not 2 which is X.
b) x (BELONGS TO) (-1,0)U(1,infinity)
c) |x|<1 This means |x| is a positive or negative fraction. Not true 1/2 divided by 1/2 = +1, not x which is 1/2 here
d) |x|=1 The question asks for "all X" meaning we must consider all possible values for x. |x| = 1 is one part of the answer, but it ignores -1 and 0. (and I guess infinity?) Since the question asks for "all X" this isn't a complete answer.
e) |x|^2>1 This looks like a filler answer where the authors just needed something for answer e). If the square of |x| is greater than 1, then x the following must be true. x < -1 or x > 1. If we eliminated d because it was an incomplete answer, then there are multiple reasons to exclude this one. -1 and 1 satisfy the question stem, but it also appears to say that x > 1 would satisfy the question also, but this isn't true. x = 2 and we already know 2 is not a valid value of x.

i could not understand the meaning.. pls explain

OA is B.

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Re: dont understand meaning... [#permalink] New post 26 Aug 2008, 10:13
Allen,

I believe question wording need to be changed.

something like this..
Find the range/all possible values of X if X/|X|=X.
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Re: dont understand meaning... [#permalink] New post 26 Aug 2008, 10:14
But the point is that for any x other than 1 or -1, the eqution will not be satisfied.

eg. x=-0.5
LHS = x/|x| = -.05/0.5 = 1 <> -0.5=RHS

eg. x= 3, LHS=1, RHS=3 LHS<>RHS

Only 1 and -1 satisfy.
x=1 then LHS=1= RHS
x=-1 then LHS=-1 = RHS.

I dont know how/why B could be the answer.
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Re: dont understand meaning... [#permalink] New post 26 Aug 2008, 10:22
is this a GMATClub challenge?
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Re: dont understand meaning... [#permalink] New post 26 Aug 2008, 11:50
This is a gmatclub question and the original poster did not post the right question.

The question states:

If \frac{X}{|X|} \lt X . Which of the following must be true for all X ?

* X > 1
* X \in (-1,0) \cup (1,\infty)
* |X| < 1
* |X| = 1
* |X|^2 > 1

For this inequality, you can multiply by |X|, because we know it's positive

So,
X < X*|X|
X - X*|X| < 0
X*(1-|X|) < 0

In order for the expression to be negative, the two components must be of opposite signs and/or not 0.
This is not true when 0< X < 1 or x < -1
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Re: dont understand meaning... [#permalink] New post 26 Aug 2008, 12:13
zoinnk wrote:
This is a gmatclub question and the original poster did not post the right question.

The question states:

If \frac{X}{|X|} \lt X . Which of the following must be true for all X ?

* X > 1
* X \in (-1,0) \cup (1,\infty)
* |X| < 1
* |X| = 1
* |X|^2 > 1

For this inequality, you can multiply by |X|, because we know it's positive

So,
X < X*|X|
X - X*|X| < 0
X*(1-|X|) < 0

In order for the expression to be negative, the two components must be of opposite signs and/or not 0.
This is not true when 0< X < 1 or x < -1



Now it makes perfect sense. < and = are two totally different ball games.
Re: dont understand meaning...   [#permalink] 26 Aug 2008, 12:13
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