GMAT Question of the day

If xy = 1, then what is the value of 2^(x+y)^2 / 2^(x-y)^2
1)8
2)4
3)2
4)16

Answer:
(x+y)^2 =(x^2+y^2+2xy)
(x-y)^2 =(x^2+y^2 - 2xy)
2^(x^2+y^2+2xy)/2^(x^2+y^2 - 2xy)
= 2^(4xy)
= 2^4
= 16