Beat The GMAT

vineetbatra · Sat Nov 07, 2009 4:10 pm

if x < 0, then root(-x|x| ) is

-x
-1
1
x
root(x)

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sanjana · Sun Nov 08, 2009 1:00 pm

IMO : -X
pick a number say x=-5
then,root(-x|x| ) = -(-5)|-5| = 5 = -x.

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vineetbatra · Sun Nov 08, 2009 1:07 pm

How is it -X, the answer is 5 and not -5. Btw -x is the OA

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sanjana · Sun Nov 08, 2009 10:09 pm

we took x as -5.The answer we got after substitution is 5 which is -(-5) = -(x).

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vijay_venky · Mon Nov 09, 2009 12:02 am

the definition for |x| goes as
|x|=-x when x<0
=x when x>0
This is the reason for the modulus of negative number to be positive.
Now -x|x|= -x*-x and this is (-x)2(square)
and sqrt((-x)2)=-x

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vineetbatra · Mon Nov 09, 2009 10:48 am

Thanks a lot Sanjana and Venky, but I am still not able to comprehend the concept.

-x where x = -5 will be -(-5) = 5

|x| where x = -5 = |-5| = 5

root(5*5) = 5. I stop here, maybe I am missing a step or a concept.

Please let me know.

Thanks again,

Vineet