GMAT Prep DS question need help

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kic883: Newbie | Next Rank: 10 Posts; Posts: 6; Joined: Tue Mar 31, 2009 3:15 am

by kic883 » Wed Apr 29, 2009 7:03 pm

Can someone explain? Thanks!

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Source: Beat The GMAT — Data Sufficiency | Wed Apr 29, 2009 7:03 pm

bluementor: Master | Next Rank: 500 Posts; Posts: 418; Joined: Wed Jun 11, 2008 5:29 am; Thanked: 65 times

by bluementor » Thu Apr 30, 2009 12:19 am

x < 0

so, -x must be positive. And since |x| is also positive:

-x|x| = x^2

The "√" symbol must only return a positive value. For example, √25 = 5 only, and not -5. Similarly:

√(x^2) = -x (positive value, since x is negative). Choose A.

hth.

-BM-

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