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colakumarfanta: Senior | Next Rank: 100 Posts; Posts: 49; Joined: Mon May 03, 2010 2:55 am; Thanked: 1 times

algebra

by colakumarfanta » Tue Nov 08, 2011 8:21 am

find [(xy)^2 - (x + y)^2]^2.
A. 32 (xy) ^ 2 B. 16 (xy) ^ 2 C. 4 (xy) ^ 2 D. 2 (xy) ^ 2 E. (xy) ^ 2

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Source: Beat The GMAT — Problem Solving | Tue Nov 08, 2011 8:21 am

user123321: Master | Next Rank: 500 Posts; Posts: 385; Joined: Fri Sep 23, 2011 9:02 pm; Thanked: 62 times; Followed by:6 members

by user123321 » Tue Nov 08, 2011 8:39 am

I am not so sure about the choices.
when I keep x = 1, y =2 , none of the choices seem to obey

user123321

Just started my preparation

Want to do it right the first time.

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Anurag@Gurome: GMAT Instructor; Posts: 3835; Joined: Fri Apr 02, 2010 10:00 pm; Location: Milpitas, CA; Thanked: 1854 times; Followed by:523 members; GMAT Score:770

by Anurag@Gurome » Tue Nov 08, 2011 8:43 am

colakumarfanta wrote:find [(xy)^2 - (x + y)^2]^2

I guess a minus sign is missing here.

[(x - y)Â² - (x + y)Â²]Â² = [-4xy]Â² = 16(xy)Â² ---> Option B

Whereas, the given expression [(xy)Â² - (x + y)Â²]Â² = [xÂ²yÂ² - xÂ² - yÂ² - 2xy]Â² is not reducible to any of the given options.

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vaibhavgupta: Master | Next Rank: 500 Posts; Posts: 416; Joined: Tue Aug 30, 2011 2:18 pm; Location: Delhi, India; Thanked: 13 times; Followed by:9 members