(x) = x + 1

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quocbao
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Topic: (x) = x + 1
PostWed Mar 25, 2009 4:03 am Reply with quote
For any integer x, (x) is defined by the equitation (x) = x + 1. Which of the following is equal to (x)*2 - (x^2) for all integers x

A. 0
B. 2
C. (2x)
D. 2x
E. 2*(x)

OA is D , but why D. I think it should be (x)^2
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moutar
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PostWed Mar 25, 2009 12:39 pm Reply with quote
(x)*2 - (x^2)
= 2[x+1] - [x^2+1]
= 2x + 2 - x^2 -1
= -x^2 + 2x + 1

If the question was (x)^2 - (x^2) then:

(x)^2 - (x^2)
= [x+1]^2 - [x^2+1]
= x^2 + 2x + 1 - x^2 - 1
= 2x
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quocbao
Rising GMAT Star



Joined: 03 Mar 2009
Posts: 88

Thanks given: 9
Thanked 3 times in 3 posts

Target GMAT Score: 720
PostFri Mar 27, 2009 9:49 am Reply with quote
Oh, I got it. thanks

darn the question
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