It is currently 23 Oct 2017, 12:08

### 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

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:

86% (00:45) correct 14% (01:41) wrong based on 214 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

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

Senior Manager
Affiliations: UWC
Joined: 09 May 2012
Posts: 393

Kudos [?]: 1617 [0], given: 100

GMAT 1: 620 Q42 V33
GMAT 2: 680 Q44 V38
GPA: 3.43
WE: Engineering (Entertainment and Sports)
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

Kudos [?]: 1617 [0], given: 100

Math Expert
Joined: 02 Sep 2009
Posts: 41913

Kudos [?]: 129489 [1], given: 12201

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

### Show Tags

10 May 2012, 01:29
1
KUDOS
Expert's post
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.
_________________

Kudos [?]: 129489 [1], given: 12201

GMAT Club Legend
Joined: 09 Sep 2013
Posts: 16534

Kudos [?]: 274 [0], given: 0

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

### Show Tags

12 Aug 2017, 03:49
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________

Kudos [?]: 274 [0], given: 0

Re: What is the value of x^2 - y^2 ?   [#permalink] 12 Aug 2017, 03:49
Display posts from previous: Sort by