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Re: a GWD math (6) , which hasn't been discussed [#permalink]
20 Aug 2011, 04:19

Jasontuyj2012 wrote:

if xy =/= 0 ( xy is not 0), is x/y=1?

(1) x^2=y^2 (2) xy>0

I chose A

1. x and y can be 1 or -1, 2 or -2 and hence x/y may or may not be =1. hence not suff 2. xy>0 .... x and y can have different values (1,1) (3,2) hence not suff

together both statements we have x and y should be of the same sign ( either -ve or +ve) and hence x/y =1. so C

Re: a GWD math (6) , which hasn't been discussed [#permalink]
20 Aug 2011, 16:15

Rephrase the question: "x = y?"

Statement 1: x^2 = y^2 implies that |x| = |y|. In the xy-plane this looks like an X (two lines) straight through the origin with slopes of 1 and -1. For xy < 0 (quadrants II and IV), y = -x. For xy > 0 (quadrants I and III), y = x.

If |x| = |y|, x does not have to equal y, it could equal -y. Insufficient.

Statement 2: xy > 0 means that any point occupies either quadrant I or III. x and y could take on any coordinate in these quadrants, such as (4,3), (1000000000000,1), (-452, -2), or (1,1), (-55,-55) etc. We do not know whether x and y are equal. Insufficient.

Combined: |x| = |y| and xy > 0, so x = y. Sufficient.