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GMAT Prep - Square root of x

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by just_do_it » Mon Sep 08, 2008 5:43 pm
since the square root of a negative number is impossible on the GMAT, the expression under square root sign has to be positive

-x|x| will be positive only if x is negative. because negative x will take care of the minus sign under square roots.

let x=-2

-(-2)|-2| = 2*2 = 4 and squre root of 4 = 2 = -(-2) = -(x)

hope this helps.
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by niraj_a » Tue Sep 09, 2008 12:47 pm
aaaahhhh such a subtle trick...
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by elem » Mon Nov 03, 2008 2:29 am
I am also confused by this quesiton and the square root function in GMAT general.

Obviously here the number is squrt (4) but that can be +2 or -2 right, or is the square root in the gmat always positive?
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Re: GMAT Prep - Square root of x

by jimmiejaz » Mon Nov 03, 2008 8:09 am
mehravikas wrote:Please explain why is the answer -x. Completely stumped by this one.
Hi vikas,

given x < 0,

and we know that |x| = -x when x < 0 and |x| = x when x > 0

so the eqn becomes
sqrt(-x(-x)) which is equal to -x. hence the choice is A.

Hope it helps!!
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by jwcwong » Sat Aug 15, 2009 7:10 am
hi Jimmy,

I still don't quite understand - according to the question sqrt-x¦x¦, shouldn't it really be sqrt(-(-x)(-x)), ie you have sqrt(x(-x))? I still don't get why the answer should be -x.. please help.
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by niraj_a » Sat Aug 15, 2009 8:06 am
test numbers. take x = -6

so the term becomes

sqrt(-(-6) * 6)
sqrt(36)
=6

x = -6
-(x) = 6 = Answer.
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by restero » Thu Jan 21, 2010 6:30 pm
Ok, read the question carefully!
It clearly says X<0; Let's assume x =-6
so though sqrt(36) = +6 or -6; X has to be -ve per the question. Hence since x<0, -X is the Answer
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