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IfSn=[1/(1+sqrt(n))+1/(2+sqrt(2n))++1/(n...

`IfS_n=[1/(1+sqrt(n))+1/(2+sqrt(2n))++1/(n+sqrt(n^2))],t h e n(lim)_(n rarr oo)S_n` is equal to (a)log 2 (b) log4 (c)log 8 (d) none of these

A

`log2`

B

`log 4`

C

`log 8`

D

none of these

Text Solution

Verified by Experts

The correct Answer is:
B
`lim_(nto oo) S_(n)=lim_(nto oo) [1/(1+sqrt(n))+1/(2+sqrt(2n))+………..+1/(n+sqrt(n)^(2))]`
`=lim_(nto oo) 1/n [1/(1/n+1/(sqrt(n)))+1/(2/n+sqrt(2/n))+……..+1/(n/n+sqrt(n/n))]`
`=int_(0)^(1)(dx)/(sqrt(x)(sqrt(x)+1))`
Put `sqrt(x)=z` or `1/(2sqrt(x))dx=dz`
`:. lim_(n to oo) S_(n)=int_(0)^(1)(2 dz)/(z+1)=2|log(z+1)|_(0)^(1)`
`=2(log2-log1)`
`=2log2=log4`
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