Need help understanding what the problem is asking for

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virtuoso902: Senior | Next Rank: 100 Posts; Posts: 42; Joined: Thu Mar 19, 2009 12:03 am; Thanked: 2 times

by virtuoso902 » Thu Oct 08, 2009 2:20 pm

Hey everyone. I Don't completely understand what this question is asking for. Also what is the most efficient way to solve this problem? Thank you ahead of time!

What is the value of X^2-Y^2?

1) x-y=0

2) x+y=4

The answer is:

A

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Source: Beat The GMAT — Data Sufficiency | Thu Oct 08, 2009 2:20 pm

JeffB: Master | Next Rank: 500 Posts; Posts: 153; Joined: Tue Jun 02, 2009 2:48 pm; Location: Ohio; Thanked: 16 times

Re: Need help understanding what the problem is asking for

by JeffB » Thu Oct 08, 2009 2:34 pm

virtuoso902 wrote:Hey everyone. I Don't completely understand what this question is asking for. Also what is the most efficient way to solve this problem? Thank you ahead of time!

What is the value of X^2-Y^2?

1) x-y=0

2) x+y=4

The answer is:

A

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

1. if x-y = 0

(x + y) (x - y)
(x + y) * 0 = always equals 0 Suff

2. if x+y = 4

(x + y) (x - y)
4 * (x-y)

InSuff.

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