BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem
TTP OnDemand GMAT Video Course
Featured Course

Target Test Prep GMAT OnDemand

Scott Woodbury-Stewart’s private virtual classroom — 400 hours of master-class video lessons for the GMAT Focus Edition.

  • 715+ score guarantee — highest in the industry (99th percentile)
  • 52 chapters · 1,500+ lessons · 4,000+ practice questions
  • 400 hours of video · 1,500+ instructor-led HD smartboard lessons
  • 300,000+ students accepted to Harvard, Stanford, Wharton, Booth & Sloan & more
  • 24/7 live support + weekly Zoom office hours with GMAT instructors
  • TTP AI Assist — 24/7 AI-powered virtual tutor for instant help
  • 1,200+ flashcards + AI-powered study assistant & daily calendar
  • OnDemand, LiveTeach & GMAT Bootcamp formats available
  • Also: GRE, SAT Math & Executive Assessment courses
  • MBA Admissions Consulting now available
  • 🏆 2025 EdTech Breakthrough Award: Test Prep Solution Provider of the Year
  • 200,000+ students served
  • 5-day free trial — $0 to start, no auto-billing, cancel anytime
★★★★★ 5.0 (559 reviews)
130-pt guarantee
$0 to start then $127/mo
Start Free 5-Day Trial Read 559 Reviews →

Imp Funda - Please Help

Expert replies
Post new topic Post Reply
Previous Topic Next Topic
Source: — Problem Solving |
Master | Next Rank: 500 Posts
Posts: 256
Joined: Mon Aug 10, 2009 6:31 pm
Thanked: 3 times

by gmatv09 » Wed Oct 21, 2009 6:20 pm
IMO D

|x| = x
-x |x| = x^2 (-x = x since x<0)

sqrt(x^2) = x
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Senior | Next Rank: 100 Posts
Posts: 63
Joined: Mon Jul 20, 2009 11:48 am
GMAT Score:730

by rainmaker » Wed Oct 21, 2009 6:31 pm
Nope. That's what I got. That's incorrect
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Junior | Next Rank: 30 Posts
Posts: 12
Joined: Wed Jul 23, 2008 6:28 am

by divyalr » Wed Oct 21, 2009 7:22 pm
Its a deceiving question.

to evaluate sqrt(-x|x|)

Take an example x= -4( x<0)

sqrt(-(-4) * |-4|) = sqrt(4 *4)= sqrt(16) = 4 (-x)

Answer is A
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Master | Next Rank: 500 Posts
Posts: 126
Joined: Wed Jun 24, 2009 1:12 pm
Location: Montreal
Thanked: 2 times
GMAT Score:510

by ssuarezo » Wed Oct 21, 2009 7:32 pm
divyalr wrote:Its a deceiving question.

to evaluate sqrt(-x|x|)

Take an example x= -4( x<0)

sqrt(-(-4) * |-4|) = sqrt(4 *4)= sqrt(16) = 4 (-x)

Answer is A
Hi:
you have x=-4, but sqrt(16) = +4, no way u get -4 as a square root.

IMO A, but for another reason, (-x|x|)=-X^2, so sqrt(-X^2) = -X, Am I wrong? What's the OA?
Thanks
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Junior | Next Rank: 30 Posts
Posts: 12
Joined: Wed Jul 23, 2008 6:28 am

by divyalr » Wed Oct 21, 2009 8:04 pm
ssuarezo wrote:
divyalr wrote:Its a deceiving question.

to evaluate sqrt(-x|x|)

Take an example x= -4( x<0)

sqrt(-(-4) * |-4|) = sqrt(4 *4)= sqrt(16) = 4 (-x)

Answer is A
Hi:
you have x=-4, but sqrt(16) = +4, no way u get -4 as a square root.

IMO A, but for another reason, (-x|x|)=-X^2, so sqrt(-X^2) = -X, Am I wrong? What's the OA?
Thanks
I did not get -4 as the square root. All I am saying is sqrt(16) = +4 ( its a negative of (x=-4) : - (-4)) which leads to (-x) Answer A
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
User avatar
Master | Next Rank: 500 Posts
Posts: 113
Joined: Sat Oct 17, 2009 10:51 am
Thanked: 10 times
GMAT Score:690

Re: Imp Funda - Please Help

by Ludacrispat26 » Wed Oct 21, 2009 9:10 pm
rainmaker wrote:If x<0, then sqrt(-x*|x|) is

A: -x
B: -1
C: 1
D: x
E: sqrt(x)

Please explain your answers.

Thanks
This is actually pretty simple.

Let x=-1

=sqrt (-(-1)*|-1|)
=sqrt (1*1)
=sqrt (1)
=1, which is -x

Let x=-2

=sqrt (-(-2)*|-2|)
= sqrt (2*2)
= sqrt (4)
= 2, which is -x

IMO A
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
User avatar
Senior | Next Rank: 100 Posts
Posts: 36
Joined: Fri Aug 28, 2009 2:40 am
Location: Singapore
Thanked: 11 times

by uttam.albela » Wed Oct 21, 2009 9:19 pm
According to OG, When you say sqrt(p*p) whether p is negative or positive, the only answer is |P|.

if you say - (sqrt(p2)), then the answer is - |P|.

So sqrt(-x * |x|) = |X| = - x

Please refer OG maths fundamentals. sqrt(9) = 3 only.

-3 is wrong.

-sqrt(9) = -3
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Senior | Next Rank: 100 Posts
Posts: 63
Joined: Mon Jul 20, 2009 11:48 am
GMAT Score:730

by rainmaker » Thu Oct 22, 2009 6:07 am
The answer is A.

divyalr, Ludacrispat26 explanation seems good
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 3380
Joined: Mon Mar 03, 2008 1:20 amFollowed by: 1535 members
Thanked: 2256 times
GMAT Score:800

by lunarpower » Mon Nov 16, 2009 2:24 am
many of the earlier posters have the easiest solution here.
since there are variables littered all over the answer choices, plugging in your own numbers is the best way to go here if you don't immediately understand the textbook method.
if you plug in ANY negative value for x, other than -1 (which will leave both (c) and (a) standing), you will instantly eliminate all answers other than (a).

this is what is done in the post by "ludacrispat26", although that poster makes the mistake of plugging in -1 as the first choice. that poster also doesn't show the trial and elimination of the answer choices.

--

by the way:

the use of "√" to represent only the positive square root is not just a gmat convention; this is an absolutely universal convention throughout ALL of mathematics.
√9 is just 3 (not 3 or -3). √16 is just 4. etc.
if x is a variable, then √(x^2) must be the positive square root. hence, √(x^2) = |x| for ALL values of x.

in this problem, since x is a negative number, |x| simplifies to -x.
Ron has been teaching various standardized tests for 20 years.

--

Pueden hacerle preguntas a Ron en castellano
Potete chiedere domande a Ron in italiano
On peut poser des questions à Ron en français
Voit esittää kysymyksiä Ron:lle myös suomeksi

--

Quand on se sent bien dans un vêtement, tout peut arriver. Un bon vêtement, c'est un passeport pour le bonheur.

Yves Saint-Laurent

--

Learn more about ron
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Post new topic Post Reply
• Page 1 of 1