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Tricky functions problem

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by tonebeeze » Tue Mar 08, 2011 3:02 pm
Please see problem attached.

OA = D

Can someone please show me their work. Thanks!
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by GMATGuruNY » Tue Mar 08, 2011 3:25 pm
tonebeeze wrote:Please see problem attached.

OA = D

Can someone please show me their work. Thanks!
Let @x = the function.
@x = x+1.

Plug in x = 10.
(@x)² - @(x²)
= (@10)² - @100
= (10+1)² - (100+1)
= 121 - 101
= 20. This is our target.

Now we plug x = 10 into all the answers to see which yields our target of 20.

Only answer choice D works:
2x = 2*10 = 20.

The correct answer is D.
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by anshumishra » Tue Mar 08, 2011 6:52 pm
tonebeeze wrote:Please see problem attached.

OA = D

Can someone please show me their work. Thanks!
@x = x+1
So, (@x)^2 - @(x^2) = (x+1)^2 - (x^2+1)
= x^2 + 2x + 1 - x^2 - 1
= 2x D
Thanks
Anshu

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