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Exponent problem

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Source: — Data Sufficiency |
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by DanaJ » Thu Feb 05, 2009 12:55 am
Let's work on the initial equation first:
(x+y)^2 = x^2 + y^2 + 2xy
(x-y)^2 = x^2 + y^2 - 2xy.

Let's use stmt 1 first: since x^2 + y^2 = 3xy, you can replace that in the initial equation and you get that it is 5xy/xy = 5. So 1 is sufficient.

2 will not be sufficient since we do not know anything about x^2 + y^2.

So I'd go with A on this one.
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by relaxin99 » Fri Feb 06, 2009 4:50 pm
This comes absolutely efortlessly to you...great, great
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by cramya » Sat Feb 07, 2009 12:18 am
Good solution Dana!

For B since x and y are not given to be integers many different values possible satisfying 0<x<y & xy=3 (x=1 y =3 x=1/3 y=9 etc..) leading to different values for (x+y)^2/(x-y)^2 so INSUFF

Choose A (xy cancels out leading in to one definite answer)
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by DanaJ » Sat Feb 07, 2009 2:06 am
Thank you guys for your kind words..
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by NicoFalcon » Sat Feb 07, 2009 2:55 am
I try to follow this advice throughly. Always when you see an equation FACTORIZE ,if it`s unfactorized, and UNFACTORIZE, if it is factorized. Always try to simplify whenever you can, and things will usually start to be clear.
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