equations

[emiflo]

hi guys. i saw this question in my last gmat test by powerprep. If xy=1, what is the ans for the following

2(x+y)(x+y) .it was a tough one. thanks.
____________
2(x-y)(x-y)

PS: The ans is 16.

[selango]

Can you check the question again..I think one condition is missing in the question.

[Stuart@KaplanGMAT]

hi guys. i saw this question in my last gmat test by powerprep. If xy=1, what is the ans for the following

2(x+y)(x+y) .it was a tough one. thanks.
____________
2(x-y)(x-y)

PS: The ans is 16.

Hi,

that's definitely not an accurate restatement of the question.

Just plug in x=y=1 (satisfying xy=1) and you get:

2(2)(2)/2(0)(0) = 8/0 which is undefined, certainly not 16.

I'm guessing that one of the conditions was that xy did NOT equal 1 and there was other information as well.

[frank1]

Just plug in x=y=1 (satisfying xy=1) and you get:

2(2)(2)/2(0)(0) = 8/0 which is undefined, certainly not 16.

I'm guessing that one of the conditions was that xy did NOT equal 1 and there was other information as well.

well sir,
am i missing something here
the question doesnt say both numbers are integer that means
x=2 and y=1/2 still validates xy=1
and i get 25/9 in that case which gives some value...

so i think outcome now depends upon assumption of number like 3 and 1/3 and so on

question is not 100% correct ...
but am i missing something in what i am doing
thanks

[Stuart@KaplanGMAT]

Just plug in x=y=1 (satisfying xy=1) and you get:

2(2)(2)/2(0)(0) = 8/0 which is undefined, certainly not 16.

I'm guessing that one of the conditions was that xy did NOT equal 1 and there was other information as well.

well sir,
am i missing something here
the question doesnt say both numbers are integer that means
x=2 and y=1/2 still validates xy=1
and i get 25/9 in that case which gives some value...

so i think outcome now depends upon assumption of number like 3 and 1/3 and so on

question is not 100% correct ...
but am i missing something in what i am doing
thanks

You could pick values that make sense - but GMAT questions have to be true for all values, not just some of them.