I will go with (A)
Question gives:
R = 1 + 2xy + x^2*y^2
Factor this to get
R = (1 + xy)(1 + xy) = (1 + xy)^2
Statement 1:
If R = 0, then either of the factors have to equal zero (and note that there is only one factor)
that means that xy = -1
Sufficient -> you know the answer.
Statement 2:
x is positive
Insufficient - this doesn't give you any indication of R or Y (or a real number for x)
No need to proceed any further and put them together, (A) was sufficient and (B) was not... there the answer is (A)
gmat prep xy
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