Arithmetic problem - unsure of the solution

by **ameya** Mon May 26, 2008 4:12 pm

If xy = 1, what is the value of : [2(x+y)^2] / [2(x-y)^2]?
Ans: 16

I am unable to get to the solution. I came across this one in the GMAT prep. I guess I am doing something silly!
Please post your solution.

Cheers
~a

by **RonPurewal** Wed Jun 04, 2008 7:23 am

yeah, that problem was mistranscribed in gmatprep for a while. the (x+y)^2 and (x-y)^2 are actually supposed to be exponents, with the 2's as their bases. so it's actually (2 to the power (x+y)^2) / (2 to the power (x-y)^2)

you subtract the exponents, and the squared terms cancel, leaving you with 2 to the power 4xy. that's 2^4 = 16.

there was another thread about this problem, but i can't find it at the moment (it's hard to find problems like this one, which has basically no keywords)