Find all School-related info fast with the new School-Specific MBA Forum

 It is currently 19 Jun 2013, 23:16

# Does x = y ? (1) x^2 - y^2 = 0 (2) (x + y)^2 = 0

Author Message
TAGS:
Director
Status: Matriculating
Affiliations: Chicago Booth
Joined: 03 Feb 2011
Posts: 947
Followers: 10

Kudos [?]: 144 [0], given: 123

Does x = y ? (1) x^2 - y^2 = 0 (2) (x + y)^2 = 0 [#permalink]  15 May 2011, 02:17
00:00

Question Stats:

22% (01:20) correct 77% (00:19) wrong based on 22 sessions
Guys
The answer sounds unconvincing. Can you verify this?

Does x = y ?
(1) x^2 - y^2 = 0
(2) (x + y)^2 = 0

[Reveal] Spoiler:
The OA is E. But I think C is the way to go. Pls verify

S1 tells us that x = -y or x = y
Insufficient

S2 tells us that x = -y or x = y = 0
Insufficient

1) + 2)
x = -y or x = y
x = -y or x = y = 0

The root x = -y satisfy both the equations. Now the trap x = -y does not preclude y from being zero. Hence x = -y can mean x = y = 0 in which case the answer is YES or it can mean x = -y in which case the answer is NO. So we cant make a conclusive statement about whether x = y

Last edited by gmat1220 on 15 May 2011, 02:27, edited 1 time in total.
Senior Manager
Joined: 03 Mar 2010
Posts: 460
Followers: 3

Kudos [?]: 76 [0], given: 21

Re: Simple yet tripping ! [#permalink]  15 May 2011, 02:27
I think this could be the reason..

Basically question is x-y=0 ?

From S1 and S2
x = -y or x = y
x = -y or x = y = 0

So either x+y=0 or x-y=0. hence cannot be determined.
_________________

My dad once said to me: Son, nothing succeeds like success.

Director
Status: Matriculating
Affiliations: Chicago Booth
Joined: 03 Feb 2011
Posts: 947
Followers: 10

Kudos [?]: 144 [0], given: 123

Re: Simple yet tripping ! [#permalink]  15 May 2011, 02:31
I think this is the trap. x = -y does not preclude y from being zero. Hence x = -y can mean x = y = 0 in which case the answer is YES or it can mean x = -y in which case the answer is NO. So we cant make a conclusive statement whether x = y

I think this could be the reason..

Basically question is x-y=0 ?

From S1 and S2
x = -y or x = y
x = -y or x = y = 0

So either x+y=0 or x-y=0. hence cannot be determined.
Math Forum Moderator
Joined: 20 Dec 2010
Posts: 2098
Followers: 109

Kudos [?]: 667 [1] , given: 376

Re: Simple yet tripping ! [#permalink]  15 May 2011, 02:39
1
KUDOS
gmat1220 wrote:
Guys
The answer sounds unconvincing. Can you verify this?

Does x = y ?
(1) x^2 - y^2 = 0
(2) (x + y)^2 = 0

Try to solve it using substitution and it will get clearer:

Q: Does x=y?

Two cases;
Case I: x != y; x=-1, y=1
Case II: x = y; x=0, y=0

(1) x^2=y^2
Case I satisfies.
Case II satisfies.
So, we have two sets both satisfying this statement. However, in one case x=y and in other x!=y. We can't conclude that x=y.

(1) x=-y
Case I satisfies.
Case II satisfies.
So, we have two sets both satisfying this statement. However, in one case x=y and in other x!=y. We can't conclude that x=y.

Combining;
The same two cases satisfy. Nothing conclusive.
Ans: "E"

If the questions said:
"Does x=y if xy!=0". Then "B" would be the answer.
_________________
Senior Manager
Joined: 31 Oct 2010
Posts: 493
Location: India
Concentration: Entrepreneurship, Strategy
GMAT 1: 710 Q48 V40
WE: Project Management (Manufacturing)
Followers: 11

Kudos [?]: 34 [0], given: 68

Re: Simple yet tripping ! [#permalink]  16 May 2011, 09:35
gmat1220 wrote:
Guys
The answer sounds unconvincing. Can you verify this?

Does x = y ?
(1) x^2 - y^2 = 0
(2) (x + y)^2 = 0

[Reveal] Spoiler:
The OA is E. But I think C is the way to go. Pls verify

S1 tells us that x = -y or x = y
Insufficient

S2 tells us that x = -y or x = y = 0
Insufficient

1) + 2)
x = -y or x = y
x = -y or x = y = 0

The root x = -y satisfy both the equations. Now the trap x = -y does not preclude y from being zero. Hence x = -y can mean x = y = 0 in which case the answer is YES or it can mean x = -y in which case the answer is NO. So we cant make a conclusive statement about whether x = y

Statement 1: tells |x|=|y|. this gives us 3 values:
a. x=y (xy not equal to 0)
b. x=-y
c. x=y=0

x and y can take infinite values.

Statement 2: tells us x=-y or x=y=0 So answer can be both "No" and "Yes"

Both statements combined, we get x=-y or x=y=0. No new information. So insufficient.

Admittedly, I almost picked B. But suddenly I remembered I had pledged that I will ALWAYS check for zero in algebra questions. Glad it paid off
_________________

My GMAT debrief: from-620-to-710-my-gmat-journey-114437.html

VP
Status: There is always something new !!
Affiliations: PMI,QAI Global,eXampleCG
Joined: 08 May 2009
Posts: 1395
Followers: 8

Kudos [?]: 86 [0], given: 10

Re: Simple yet tripping ! [#permalink]  16 May 2011, 10:40
yup we need to check for 0 too here.

x= -y, x=y=0 both creeps in, in a and b.

hence E.
_________________

Visit -- http://www.sustainable-sphere.com/
Promote Green Business,Sustainable Living and Green Earth !!

Manager
Status: GMAT in 4 weeks
Joined: 28 Mar 2010
Posts: 194
GPA: 3.89
Followers: 1

Kudos [?]: 22 [0], given: 25

Re: Simple yet tripping ! [#permalink]  17 May 2011, 11:07
very tricky ...

I also pledged that I will ALWAYS check for zero in algebra questions.
_________________

If you liked my post, please consider a Kudos for me. Thanks!

Manager
Joined: 28 Jul 2011
Posts: 115
Followers: 0

Kudos [?]: 1 [0], given: 6

Re: Simple yet tripping ! [#permalink]  03 Nov 2011, 13:05
Should E. tricky zeros
Re: Simple yet tripping !   [#permalink] 03 Nov 2011, 13:05
Similar topics Replies Last post
Similar
Topics:
Does x=y? 1) x^2 - y^2 = 0 2) (x+y)^2 = 0 2 13 Apr 2006, 15:42
Does X=Y? 1) X^2-Y^2=0 2) (X+Y)^2=0 10 18 Oct 2006, 13:28
0<X<Y What does (X+Y)^2/(X-Y)^2 = (1) X^2 +Y^2 = 3XY 9 13 May 2007, 16:50
1 Does x = y? (1) x^2 - y^2 = 0 (2) (x - y)^2 = 0 11 29 Apr 2011, 07:21
1 Does x = y ? (1) x^2-y^2=0 (2) (x+y)^2=0 6 24 Jul 2011, 15:32
Display posts from previous: Sort by