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If x < y, is square(x) < square(y)?

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Source: — Data Sufficiency |
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by clock60 » Sat Sep 25, 2010 9:25 am
my humble try
if x<y is x^2<y^2, after little transforming
is x^2-y^2<0
is (x-y)(x+y)<0. two cases are possible
1) x-y>0 x>y but accrding to the problem x<y so
2) x-y<0, x<y and x+y>0 and now the question: is x+y>0

(1) y>0 if y>0 x can be also >0 or <0 not suffiicent
x=2,y=3 x+y>0
y=3, x=-4 x+y<0

(2) is x>0 then y must be>0 as x<y and x+y will be always +ve

so my pick for B
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by GMATMadeEasy » Sat Sep 25, 2010 11:40 am
very well done
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