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# What is the value of X^2 -Y^2? 1. x+y=2x 2. x+y=0 I

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Senior Manager
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What is the value of X^2 -Y^2? 1. x+y=2x 2. x+y=0 I [#permalink]  17 Jul 2006, 20:59
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What is the value of X^2 -Y^2?

1. x+y=2x
2. x+y=0

I understand how 2 is sufficent but I am confused about stem 1 because the answer, according to the key, is D...
VP
Joined: 25 Nov 2004
Posts: 1495
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Re: DS GMAT Plus [#permalink]  17 Jul 2006, 21:17
jamesrwrightiii wrote:
What is the value of X^2 -Y^2?

1. x+y=2x
2. x+y=0

I understand how 2 is sufficent but I am confused about stem 1 because the answer, according to the key, is D...

agreed that its D but its not a good question.

1. x+y=2x
x = y. so x^2-y^2 = 0. suff.

2. x+y=0
x = -y. x and y have same values but just opposite signs. since squaring these variables eliminates the sign problems and gives x^2-y^2 = 0. also suff.
Senior Manager
Joined: 02 May 2004
Posts: 313
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Thank you!:)
I feel stupid now haha
It was a simple question
GMAT Club Legend
Joined: 07 Jul 2004
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St1:
(x+y) = 2x --> THen we have x^2-y^2 = (x+y)(x-y) = (2x)(x-y) --> Insufficient.

St2:
(x+y) = 0, then x^2-y^2 = (x+y)(x-y) = 0 --> Sufficient.

Ans B
VP
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Yes agree with D.
Statement 1-----> x+y = 2x , => x = y ;........sufficient

Statement 2-----> x +y = 0 , => x = - y;.......sufficient.
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