Square root

Expert replies

gmat740: MBA Student; Posts: 1194; Joined: Sat Aug 16, 2008 9:42 pmFollowed by: 17 members; Location: Paris, France; Thanked: 71 times; GMAT Score:710

by gmat740 » Mon Apr 06, 2009 9:48 pm

please explain why x is not the answer

I did ask this question earlier,but since the form of the question was not clear so I am asking again

Attachments

Like this post

Source: Beat The GMAT — Problem Solving | Mon Apr 06, 2009 9:48 pm

scoobydooby: Legendary Member; Posts: 1035; Joined: Wed Aug 27, 2008 10:56 pmFollowed by: 1 member; Thanked: 104 times

by scoobydooby » Mon Apr 06, 2009 10:56 pm

i would pick a number. since x<0, say x=-2

(-x*|x|)^1/2= [-(-2)*|-2|]^1/2
=> (2*2)^1/2
=2 (a square root is always +ive or 0. (non-negative)

so the expression translates to -x

Like this post

gmat740: MBA Student; Posts: 1194; Joined: Sat Aug 16, 2008 9:42 pmFollowed by: 17 members; Location: Paris, France; Thanked: 71 times; GMAT Score:710

by gmat740 » Mon Apr 06, 2009 11:09 pm

=2 (a square root is always +ive or 0. (non-negative)

The number inside the square root has to be always positive,however the result that is, the answer obtained by taking square root can be positive or negative

You need to brush up your skills again scoobydbooby

Like this post

scoobydooby: Legendary Member; Posts: 1035; Joined: Wed Aug 27, 2008 10:56 pmFollowed by: 1 member; Thanked: 104 times

by scoobydooby » Mon Apr 06, 2009 11:20 pm

for the gmat the number inside the square root has to be positive as otherwise we would be dealing with complex numbers which are not tested on the gmat.

and √(x^2) is equal to |x|. so √(2^2) is always |2| or +2

gmat740,
that was outright rude. always choose your words with caution, you never know when you have to eat them.

Like this post

anshulseth: Master | Next Rank: 500 Posts; Posts: 145; Joined: Mon Feb 16, 2009 8:41 amFollowed by: 2 members; Thanked: 2 times

by anshulseth » Tue Apr 07, 2009 1:17 am

Now, now, here's the exact reason:

For all real numbers x,
sqrt{x^2} = |x| = x , if x > 0
= -x, if x < 0

As x<0, so answer is -x.

Asset

Like this post

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

by bluementor » Tue Apr 07, 2009 2:00 am

gmat740, you shouldn't say things like that about other forum members.

As for this problem, I see that you have made a similar reasoning in this post:

https://www.beatthegmat.com/gmat-prep-1- ... tml#139267

I've given the same explanation as what scoobydooby has given here.

-BM-

Like this post

Post new topic Post Reply

• Page 1 of 1

GMAT Course Reviews

560 reviews

1168 reviews

431 reviews

359 reviews

147 reviews

5/5

5 Star (560 Reviews)

"Target Test Prep is the closest to the official version of the GMAT exam, about 99% accuracy in terms of the quality and quantity of information. The course has excellently created singular sets of focused lessons and tests for every possible topic that one could come across in the official GMAT exam."

"The TTP course maximizes the efficiency of the time you spend studying. It will take time and effort but I could almost guarantee that if you complete the course exactly as it is laid out you will get an amazing score. They also have a very responsive team willing to help with any questions you might have."

"TTP has two things that I think no other test prep company offers: A teaching approach that reinforces understanding and an attitude that will give you the mental preparedness needed to succeed on the test. TTP gives you a deep understanding of the concept you need to know while teaching you how to think."

Write a Review