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Hi All,

This DS question is built around some common Algebra patterns that you're likely to face on Test Day.

We're asked for the value of X-Y.

Fact 1: 2XY - Y^2 = X^2

The squared terms should remind you of a Classic Quadratic. Moving the 'pieces' around gets us....

0 = X^2 - 2XY + Y^2

This can be factored down into....

0 = (X-Y)^2

0 = (X-Y) so we have the only answer to the question.
Fact 1 is SUFFICIENT

Fact 2: Y^2 = -X^2

Moving the pieces here gets us...

X^2 + Y^2 = 0

Since a squared term is either 0 or positive, the ONLY way for X^2 + Y^2 to equal 0 is if they are BOTH equal to 0

So X^2 = 0 means that X = 0
Y^2 = 0 means that Y = 0

The answer to the question is 0 - 0 = 0
Fact 2 is SUFFICIENT

Final Answer:
GMAT assassins aren't born, they're made,
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What is the value of x - y ?

(1) 2xy - y^2 = x^2
(2) y^2 = -x^2

1. rewrite: x^2 + y^2 - 2xy = 0 => (x-y)^2 = 0. x-y=0
2. a number, regardless of whether it is positive or negative, can never be negative when squared. this gives only 1 option = y and x are equal to 0. thus x-y = 0.

D.
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In both the cases, the value of x-y will be zero.
hence, both statements are sufficient
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