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New post 22 Jul 2006, 12:07
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 =?

The answer is -x.
My ques is why not x both are choices.

Pravin
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New post 22 Jul 2006, 12:11
discussed recently. Very good question.

http://www.gmatclub.com/phpbb/viewtopic.php?t=32092
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New post 22 Jul 2006, 12:21
pravinkawadkar wrote:
If x<0 then (-x|x|)^1/2 =?

The answer is -x.
My ques is why not x both are choices.

Pravin


GMAT doesn't cover imaginary numbers!!
Thus, sqrt(?) > 0 always!! also ? > 0 always!!

(-x*-x)^1/2 = (x^2)^1/2 = -x
if you not sure, try to plug in any negative interger. ex. -1
given eq.
(1*1)^1/2 = 1 : -x = -(-1) = 1
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New post 22 Jul 2006, 14:43
it would help if you posted the question in its entirety :)

Nice link, ps_dahiya....something new:

Let me see if I understand it correctly -

(-x|x|)^1/2 is our expression, and x is negative.

From the answer choices, the others are clearly out apart from x and -x. If x is the root, then we get the expression as sqrt (-(x).x)^1/2, which is the square root of a negative number. By definition this is impossible.

If the root is -x, then we get the expression as sqrt(-(-x).x)^1/2 which is the sqrt of a +ve number.

Ok
  [#permalink] 22 Jul 2006, 14:43
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