Find all School-related info fast with the new School-Specific MBA Forum
Learn more about the recent changes... close

It is currently 25 May 2013, 12:55
Customize  |  Hide

Search
Register
New posts
Unanswered

M15#37

  Question banks Downloads My Bookmarks Reviews  
  Oldest Best Reply
Search for:
 
Print view
First unread post
Author Message
Manager
Manager
Joined: 29 Sep 2008
Posts: 157
Followers: 2

Kudos [?]: 8 [0], given: 1

GMAT Tests User
M15#37 [#permalink] New post 25 May 2012, 09:28
00:00

Question Stats:

33% (02:16) correct 66% (00:00) wrong based on 0 sessions
there is a question in test m15

a^2-b^2=b^2-c^2.Is a=|b|

1)b=|c|
2)b=|a|

from 1 we get a^2=b^2

a=root b^2

or a=|b|

but in answer its given

a^2=b^2
so |a|=|b|


i have doubt regarding mod

|a|=root a^2

so above how can we write a^2=|a|
[Reveal] Spoiler: OA
2 KUDOS received
GMAT Club team member
User avatar
Joined: 02 Sep 2009
Posts: 11633
Followers: 1802

Kudos [?]: 9611 [2] , given: 829

GMAT Tests User CAT Tests
Top Member of the Month
Re: M15#37 [#permalink] New post 25 May 2012, 12:45
2
This post received
KUDOS
mrinal2100 wrote:
there is a question in test m15

a^2-b^2=b^2-c^2.Is a=|b|

1)b=|c|
2)b=|a|

from 1 we get a^2=b^2

a=root b^2

or a=|b|

but in answer its given

a^2=b^2
so |a|=|b|


i have doubt regarding mod

|a|=root a^2

so above how can we write a^2=|a|


I guess your main question is about the following issue is why is \sqrt{x^2}=|x| true.

The point here is that as square root function can not give negative result then \sqrt{some \ expression}\geq{0}.

So \sqrt{x^2}\geq{0}. But what does \sqrt{x^2} equal to?

Let's consider following examples:
If x=5 --> \sqrt{x^2}=\sqrt{25}=5=x=positive;
If x=-5 --> \sqrt{x^2}=\sqrt{25}=5=-x=positive.

So we got that:
\sqrt{x^2}=x, if x\geq{0};
\sqrt{x^2}=-x, if x<0.

What function does exactly the same thing? The absolute value function: |x|=x, if x\geq{0} and |x|=-x, if x<0. That is why \sqrt{x^2}=|x|.

Hope it helps.
_________________

PLEASE READ AND FOLLOW: 11 Rules for Posting!!!

RESOURCES: [GMAT MATH BOOK]; 1. Triangles; 2. Polygons; 3. Coordinate Geometry; 4. Factorials; 5. Circles; 6. Number Theory

COLLECTION OF QUESTIONS:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. NEW!!!

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS ; 9 Devil's Dozen!!!; 10 Number Properties set. NEW!!!


What are GMAT Club Tests?
25 extra-hard Quant Tests

Find out what's new at GMAT Club - latest features and updates

Manager
Manager
User avatar
Joined: 01 Nov 2010
Posts: 204
Location: India
Concentration: Technology, Marketing
GMAT Date: 08-27-2012
GPA: 3.8
WE: Marketing (Manufacturing)
Followers: 5

Kudos [?]: 10 [0], given: 26

GMAT Tests User
Re: M15#37 [#permalink] New post 27 May 2012, 02:17
mrinal2100 wrote:
there is a question in test m15

a^2-b^2=b^2-c^2.Is a=|b|

1)b=|c|
2)b=|a|

from 1 we get a^2=b^2

a=root b^2

or a=|b|

but in answer its given

a^2=b^2
so |a|=|b|


i have doubt regarding mod

|a|=root a^2

so above how can we write a^2=|a|



here,
a^2=b^2
==> |a|=|b|
because here a &b both are variable.

|a|=root a^2; in all cases, but when you are equating a variable to variable a^2=b^2,
==> |a|=|b|, you have to right it this way.
_________________

kudos me if you like my post.

Attitude determine everything.
all the best and God bless you.

Re: M15#37   [#permalink] 27 May 2012, 02:17
Display posts from previous: Sort by

M15#37

  Question banks Downloads My Bookmarks Reviews  
Print view
First unread post

Moderator: Bunuel

Search for:


GMAT Club MBA Forum Home| About| Privacy Policy| Terms and Conditions| GMAT Club Rules| Contact| Sitemap

Powered by phpBB © phpBB Group and phpBB SEO

Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.

Main navigation

GMAT Resources

Partners

MBA Resources

www.gmac.com|www.mba.com