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Quant - 1

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Manager
Joined: 21 Feb 2009
Posts: 108

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26 Mar 2009, 11:59
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This topic is locked. If you want to discuss this question please re-post it in the respective forum.

If x<0,then (-x|x|)^1/2
1. -x
2. -1
3. 1
4. x
5. x^1/2
Senior Manager
Joined: 16 Jan 2009
Posts: 355
Concentration: Technology, Marketing
GMAT 1: 700 Q50 V34
GPA: 3
WE: Sales (Telecommunications)

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26 Mar 2009, 12:16
for (-x|x|)^1/2,

for x<0 , -x|x| = x^2
So , (-x|x|)^1/2= x

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Lahoosaher

Manager
Joined: 19 May 2008
Posts: 162
Location: Mumbai

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26 Mar 2009, 12:19
Let's say x is -1
Then (-(-1)|-1|)^1/2 = (1)^1/2 = -1 or 1
Same is the case with 2, it would be -2 or 2

So what's the OA? Is it D?
Manager
Joined: 19 May 2008
Posts: 162
Location: Mumbai

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26 Mar 2009, 12:20
Ok got it now - (x ^ 2)^1/2 = x. It should be D.
Manager
Joined: 21 Feb 2009
Posts: 108

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26 Mar 2009, 12:22
This is a question from GMATPrep.
And they say answer is -x.

I don't understand how could it be -x.
Senior Manager
Joined: 16 Jan 2009
Posts: 355
Concentration: Technology, Marketing
GMAT 1: 700 Q50 V34
GPA: 3
WE: Sales (Telecommunications)

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26 Mar 2009, 12:27
MGMAT book says that for an even root , a non negative rooot of a number is valid .
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Lahoosaher

Manager
Joined: 19 May 2008
Posts: 162
Location: Mumbai

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26 Mar 2009, 12:39
Ok what we get as the final answer is x
But we started with x < 0
and what is the answer x - it is nothing other than -x. ie., - (-x) or -(-2)

So GMATPrep is correct - the answer is A
Funny how these questions can be the difference between above/below 700.
Manager
Joined: 21 Feb 2009
Posts: 108

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26 Mar 2009, 14:28
Nice Explanation...!!
Re: Quant - 1   [#permalink] 26 Mar 2009, 14:28
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