simple but cnt understand

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manasi_sh: Senior | Next Rank: 100 Posts; Posts: 69; Joined: Sat Sep 15, 2007 1:54 am

by manasi_sh » Sun Oct 07, 2007 7:30 am

Is x2 equal to xy?
(1) x2 – y2 = (x + 5)(y - 5)
(2) x = y
Ans B..
x2= x square and y2 = y square

Source: Beat The GMAT — Data Sufficiency | Sun Oct 07, 2007 7:30 am

santsark: Newbie | Next Rank: 10 Posts; Posts: 6; Joined: Tue Sep 25, 2007 1:03 am

by santsark » Tue Oct 09, 2007 11:00 pm

From 1 you can get the value of Y, which is not sufficient to prove X^2 = XY.

But from 2 we know X=Y, so XY = X*X = X^2.

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