Official GMATprep trial exam question 2

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by Brent@GMATPrepNow » Mon Oct 30, 2017 8:24 am
if xy=1 then what is the value of 2^(x+y)²/ 2^(x-y)²

1)2
2) 4
3) 8
4) 16
5) 32
2^(x+y)²/ 2^(x-y)² = 2^(x² + 2xy + y²)/ 2^(x² - 2xy + y²)
= 2^(4xy) [after we SUBTRACT exponents]
= 2^4 [since xy = 1]
= 16

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by Matt@VeritasPrep » Thu Nov 09, 2017 6:02 pm
Or cheat a bit and pick numbers that satisfy xy = 1, such as ... I dunno, x = 1, y = 1 :D

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