options ?

Picking numbers is the best strategy for this problem.

Since you are told xy=1, you know that either:

1)x and y both = 1 or -1

or

2) x and y are reciprocols(ex. 2 and 1/2)

since

the denominator has (x-y)^2

using (1) would give 0^2 = 0 making the expression undefined which means (2) must be true.

So, just pick simple numbers for x and y like 2 and 1/2 and plug them in to the expression above.

The find the answer choice that gives you the same number and that is your answer.

HTH

thank you

thanks