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`IfS_n=[1/(1+sqrt(n))+1/(2+sqrt(2n))++1/(n+sqrt(n^2))],t h e n(lim)_(nvecoo)S_n`is equal tolog 2 (b) log4log 8 (d) none of theseA. `log2`B. `log 4`C. `log 8`D. none of these |
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Answer» Correct Answer - 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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