Check GMAT Club Decision Tracker for the Latest School Decision Releases https://gmatclub.com/AppTrack

 It is currently 29 May 2017, 14:34

### GMAT Club Daily Prep

#### Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

# What is the value of x^2 - y^2 ?

Author Message
TAGS:

### Hide Tags

Intern
Joined: 14 Mar 2012
Posts: 11
Followers: 0

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

What is the value of x^2 - y^2 ? [#permalink]

### Show Tags

10 May 2012, 00:07
1
This post was
BOOKMARKED
00:00

Difficulty:

5% (low)

Question Stats:

84% (01:46) correct 16% (01:11) wrong based on 160 sessions

### HideShow timer Statistics

What is the value of x^2 - y^2 ?

(1) x - y = y + 2
(2) x - y = 1 / (x+y)

OG Quant Review - 2nd Edition - DS-Question 46

This is an official question. OA and answer explanation is available.
My query is for second condition. How can we mutiply both sides by (x+y) unless it is specified that x+y is not equal to zero or x not equal to -y. Should we assume that denominator is not equal to zero in such GMAT questions ?
[Reveal] Spoiler: OA
Senior Manager
Affiliations: UWC
Joined: 09 May 2012
Posts: 393
GMAT 1: 620 Q42 V33
GMAT 2: 680 Q44 V38
GPA: 3.43
WE: Engineering (Entertainment and Sports)
Followers: 31

Kudos [?]: 1285 [0], given: 100

Re: DS- Multiplication by zero [#permalink]

### Show Tags

10 May 2012, 00:53
Statement 2 itself gives you this answer:

Since (x-y) = 1/(x+y)
(x-y) (x+y) = 1
For this to be true, (x-y) cannot equal 0 and likewise, (x+y) cannot equal 0
Math Expert
Joined: 02 Sep 2009
Posts: 39062
Followers: 7755

Kudos [?]: 106571 [0], given: 11628

Re: What is the value of x^2 - y^2 ? [#permalink]

### Show Tags

10 May 2012, 01:29
What is the value of x^2 - y^2 ?

(1) x - y = y + 2 --> x=2y+2, so x^2-y^2=(y+2)^2-y^2 --> to get the value of this expression we need to know the value of y. Not sufficient.

(2) x - y = 1 / (x+y) --> cross-multiply: (x-y)(x+y)=1 --> x^2-y^2=1. Sufficient.

As for your doubt: since x+y is in denominator it cannot equal to zero (because if it does equal zero then 1/(x+y) won't be defined).

Hope it's clear.
_________________
Re: What is the value of x^2 - y^2 ?   [#permalink] 10 May 2012, 01:29
Similar topics Replies Last post
Similar
Topics:
What is the value of (y^2–x^2)/(x^2y^2) 1 23 May 2017, 00:57
5 What is the value of x^2 - y^2? 10 14 Jul 2016, 14:24
What is the value of 6y + 2x^2 ? 6 15 Aug 2016, 03:41
7 What is the value of x^2 + y^2 ? 11 06 Jul 2016, 06:39
2 What is the value of x^2 + y^2 ? 7 02 Dec 2014, 00:56
Display posts from previous: Sort by