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GMAT PREP (I tried the search, couldn't find it again)

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Re: GMAT PREP (I tried the search, couldn't find it again)

by Morgoth » Wed Oct 01, 2008 6:57 pm
smclean23 wrote:If xy=1, what is the value of 2^(x+y)^2/2^(x-y)^2


OA is D.

PLEASE EXPLAIN.

2^(x+y)^2/2^(x-y)^2

Numerator = 2^(x+y)^2 = 2^(x^2 + y^2 + 2xy) = 2^x^2 * 2^y^2 * 2^2xy

Denominator = 2^(x-y)^2 = 2^(x^2 + y^2 - 2xy) = 2^x^2 * 2^y^2 / 2^2xy

2^x^2 * 2^y^2 * 2^2xy / 2^x^2 * 2^y^2 / 2^2xy


2^2xy * 2^2xy = 2^2 * 2^2 = 4 * 4 = 16
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