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Does square(x) = y ?

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Source: — Data Sufficiency |
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by clock60 » Sat Sep 25, 2010 9:38 am
here i got A with below reasoning
i hope that it looks like
does x^2=y , little math, y=(y^1/2)^2
does x^2-(y^1/2)^2=(x-y^1/2)(x+y^1/2)=0, the given equality will be right if
x=y^1/2, or x=-(y^1/2). to the statements

(1) y^1/2=-x, this coincides with x=-(y^1/2) so i think suff
(2) many cases are possible
x<y x=2, y=4 2^2=4 yes
x=1, y=4 1^2 not equal 4 insuff
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by GMATMadeEasy » Sat Sep 25, 2010 11:30 am
wonderful. your solutions are good.
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by GMATMadeEasy » Sat Sep 25, 2010 11:32 am
can we do it this way :

sqrt(y) = -x ; do square both sides - > Y = square(X) ?
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