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# GMAT Prep: PS (Factoring)

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Senior Manager
Joined: 05 Mar 2006
Posts: 348

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07 Aug 2006, 05:33
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Senior Manager
Joined: 14 Jul 2005
Posts: 402

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07 Aug 2006, 08:21
This question is wrong...

It should be 2^(x+y)^2/2^(x-y)^2

which will give you 2^4xy = 2^4 = 16
Senior Manager
Joined: 05 Mar 2006
Posts: 348

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08 Aug 2006, 06:41
Thanks gmatornot.

I was going nuts tryin to figure this one out. When I took the GMATprep and this question showed up I wasted 10 minutes before I gave up and guessed. Then I went back and tried to work it out again, still kept hitting a dead end.
Manager
Joined: 08 May 2004
Posts: 158
Location: Pittsburgh

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09 Aug 2006, 18:52
I did it the long way...
I multiplied both out and got

2x^2+4xy+2y^2
--------------------
2x^2-4xy+2y^2

When you divide out, you get

4xy
------
-4xy

I know the answer is 16. When I bring the 4xy on the bottom up to the top why doesn't it equal 16?
Manager
Joined: 12 May 2006
Posts: 116

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10 Aug 2006, 14:49
Quote:
2x^2+4xy+2y^2
--------------------
2x^2-4xy+2y^2

I am not sure how you got 2x^2 and 2y^2, but regardless, once you have that, and since this is an exponent, you will subtract the denominator from the numerator:

x^2 + 2xy + 2y^2 - x^2 + 2xy - y^2

=4xy= 4

2^4
Manager
Joined: 08 May 2004
Posts: 158
Location: Pittsburgh

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10 Aug 2006, 20:37
ps_dahiya wrote:
jamesrwright3 wrote:
I did it the long way...
I multiplied both out and got

2x^2+4xy+2y^2
--------------------
2x^2-4xy+2y^2

When you divide out, you get

4xy
------
-4xy

I know the answer is 16. When I bring the 4xy on the bottom up to the top why doesn't it equal 16?

How did you divide????

Am I not allowed to divide the like terms on the top and bottom?
Manager
Joined: 08 May 2004
Posts: 158
Location: Pittsburgh

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10 Aug 2006, 20:39
rdw28 wrote:
Quote:
2x^2+4xy+2y^2
--------------------
2x^2-4xy+2y^2

I am not sure how you got 2x^2 and 2y^2, but regardless, once you have that, and since this is an exponent, you will subtract the denominator from the numerator:

x^2 + 2xy + 2y^2 - x^2 + 2xy - y^2

=4xy= 4

2^4

I got it by simply squaring the x-y and the x+y on the tops and bottom and then multiplying the result by 2
CEO
Joined: 20 Nov 2005
Posts: 2894
Schools: Completed at SAID BUSINESS SCHOOL, OXFORD - Class of 2008

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10 Aug 2006, 22:44
jamesrwright3 wrote:
ps_dahiya wrote:
jamesrwright3 wrote:
I did it the long way...
I multiplied both out and got

2x^2+4xy+2y^2
--------------------
2x^2-4xy+2y^2

When you divide out, you get

4xy
------
-4xy

I know the answer is 16. When I bring the 4xy on the bottom up to the top why doesn't it equal 16?

How did you divide????

Am I not allowed to divide the like terms on the top and bottom?

Not by splitting them.....
(2a+b)/(a+b) can be handled as
(a+a+b)/(a+b) = [a/(a+b)] +1 but you can not divide just a by a and by by b.

In summary you can split numerator but can't split denominator.
_________________

SAID BUSINESS SCHOOL, OXFORD - MBA CLASS OF 2008

10 Aug 2006, 22:44
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