Quadratics

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tonebeeze: Master | Next Rank: 500 Posts; Posts: 158; Joined: Mon Nov 02, 2009 5:49 pmFollowed by: 3 members; Thanked: 2 times

by tonebeeze » Tue Mar 08, 2011 7:53 am

What is the value of xy?

1. (x + y)^2 = 37
2. (x - y)^2 = 17

OA = C

Can someone walk me through the math please. Thanks.

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Source: Beat The GMAT — Data Sufficiency | Tue Mar 08, 2011 7:53 am

kmittal82: Master | Next Rank: 500 Posts; Posts: 324; Joined: Mon Jul 05, 2010 6:44 amFollowed by: 3 members; Location: London; Thanked: 70 times

by kmittal82 » Tue Mar 08, 2011 7:59 am

expand 1

x^2 + y^2 + 2xy = 37

expand 2

x^2 + y^2 - 2xy = 17

Subtract the two:

4xy = 20
xy = 5

Enough info to answer the question

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