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Master | Next Rank: 500 Posts
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by jeffedwards » Wed Nov 11, 2009 6:51 pm
If n is positive, which of the following is equal to 1/((√(n+1)) - √n)
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    √(2n+1)
    √(n+1)/√n
    √(n+1) - √n
    √(n+1) = √n

I understand how the OG explains the answer, but do you have any simpler tips?

OA: E
Source: OG 12th E; PS #117
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by antondesh » Thu Nov 12, 2009 11:50 am
Multiply the whole equation by
(√(n+1) + √n)/(√(n+1) + √n)

You'll get:
(√(n+1) + √n)/(n + 1 - n)

Which is just:
√(n+1) + √n


This is basically testing whether you know that (x-y)*(x+y)= x^2 - y^2
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by jeffedwards » Thu Nov 12, 2009 5:28 pm
thanks a million. that is so simple. I should have known they were testing for that. i've got to be on the lookout for GMAC's little tricks. Thanks a ton!!
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