Prob Solving - Help reqd

Hi All

I took a practice GMAT test from the prep files. I got the below
question and wasnt able to solve it. Please help me.

If xy = 1, what is the value of

{2* (x+y)^2} / {2* (x-y)^2}

The answer option given are,

a) 2, b) 4, c) 8, d) 16, e) 32

And they claim that correct answer is d) 16

Please let me know how to get this correct.

Thanks,
Sathish

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