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A problem

by SpeCTRuM » Tue Sep 23, 2008 11:35 am
Hello,

I could not understand the below question;


Image


The correct answer is A but i just can not understand why.

If the first "is" were "if", i should understand. Because then, if x <> 0, y had to be 0 to show that the first proposition is true. But i just confused because of the first sentence.
Is xy + z, is |x-y| >0?
Could anyone explain the sentence and the solution?

Thanks...
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by 4meonly » Tue Sep 23, 2008 11:42 am
I think question should be
If xy + z = z, is |x-y| >0?
Reprasing the question we should answer x is not equeal to y? (from |x-y| >0?)
From If xy + z = z we conclude that xy=0
so we can have
x=0, y=0
x=0, y -any number
x-any number, y=0

(1)
x is not equal to zero, so y=0
so, difference between x and y is not equal to zero, |x-y| >0
SUFF

(2)
y=0
two options
x=0, y=0. |x-y| = 0
x-any number, y=0. |x-y| >0
INSUFF

Answer A
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