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og 117- help

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by ashblog02 » Wed Nov 10, 2010 9:25 am
if n is +ve which of the following is equal to
1/ sq root of n+1 - sq root of n

1.1
2.sq root 2n+1
3.sq rt n+1 / sq rt n
4.sq root of n+1 - sq root of n
5.sq root of n+1 + sq root of n

i understood the explanation but why is it not 1
i sq the equations the n cancels put 1 /1 ans is 1
I want to know what is wrong with tht methord
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Source: — Data Sufficiency |

by selango » Wed Nov 10, 2010 9:34 am
Is it 1/(sqrt(n+1)-sqrt(n))?

1/(sqrt(n+1)-sqrt(n))

Multiply by (sqrt(n+1)+sqrt(n)) on both numerator on denominator


(sqrt(n+1)+sqrt(n)) / [ (sqrt(n+1)-sqrt(n)) * (sqrt(n+1)+sqrt(n))]

we know (a+b)(a-b)=a^2-b^2


(sqrt(n+1)+sqrt(n)) / [ (sqrt(n+1))^2 - (sqrt(n))^2]

(sqrt(n+1)+sqrt(n)) / (n+1-n)

sqrt(n+1)+sqrt(n)

Pick E
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by selango » Wed Nov 10, 2010 9:35 am
Sorry.I request the moderator to move this question to PS section.
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