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

Redeem

Squaring

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Master | Next Rank: 500 Posts
Posts: 186
Joined: Sat Jan 26, 2008 10:05 pm
Thanked: 2 times

Squaring

by medea66 » Mon Aug 11, 2008 8:00 pm
I picked numbers for this one(perfect squares), but I guess not the right numbers since they don't work out with the given solution.......
Attachments
Squares.JPG
Top
Source: — Problem Solving |
Legendary Member
Posts: 829
Joined: Mon Jul 07, 2008 10:09 pm
Location: INDIA
Thanked: 84 times
Followed by:3 members

by sudhir3127 » Mon Aug 11, 2008 8:06 pm
Plug in the values...
i took a=2 and b =1

hence sqroot(a^2-b^2) = sqrt(2^2-1^2)=sqrt(3)

only option D gives me sqrt(3).

hope it helps..
Top
Master | Next Rank: 500 Posts
Posts: 418
Joined: Wed Jun 11, 2008 5:29 am
Thanked: 65 times

by bluementor » Tue Aug 12, 2008 5:45 am
I'm not sure if my approach would be ideal for other similar questions, but here it goes:

sqrt(a^2 - b^2)
= sqrt((a-b)(a+b))
= sqrt(a-b)*sqrt(a+b)

BlueMentor
Top
Senior | Next Rank: 100 Posts
Posts: 48
Joined: Fri Aug 08, 2008 4:44 am
Thanked: 4 times
GMAT Score:750

by santa_dem » Tue Aug 12, 2008 5:52 am
Just remember that x^2-y^2=(x+y)*(x-y).

Simple as that.
Top
Master | Next Rank: 500 Posts
Posts: 186
Joined: Sat Jan 26, 2008 10:05 pm
Thanked: 2 times

by medea66 » Tue Aug 12, 2008 5:56 pm
I think the mistake I made is that I felt compelled to pick perfect squares for A & B, and in the process I complicated the calculation.

The calculation is alot simpler if I pick just 1 & 2 for A & B, respectively.
Top

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 2623
Joined: Mon Jun 02, 2008 3:17 am
Location: Montreal
Thanked: 1090 times
Followed by:355 members
GMAT Score:780

by Ian Stewart » Tue Aug 12, 2008 7:57 pm
santa_dem wrote:Just remember that x^2-y^2=(x+y)*(x-y).

Simple as that.
Exactly. You will see a difference of squares on your GMAT, guaranteed. Be sure you can recognize it, and factor it when it shows up. If you notice, in this question, that the expression under the root is a difference of squares, the problem is straightforward- much faster than choosing numbers.
For online GMAT math tutoring, or to buy my higher-level Quant books and problem sets, contact me at ianstewartgmat at gmail.com

ianstewartgmat.com
Top
Post new topic Post Reply
• Page 1 of 1