1.

The sum to infinity of the series `1+2(1-(1)/(n))+3(1-(1)/(n))^(2)+ . . .. . . .`, isA. `n^(2)`B. `n(n+1)`C. `n(1+(1)/(n))^(2)`D. None of these

Answer» Correct Answer - A
Let `S=1+2(1-(1)/(n))+3(1-(1)/(n))^(2)+"...."+oo`
`((1-(1)/(n))S=(1-(1)/(n))+2(1-(1)/(n))+"...."+oo)/(S(1-1+(1)/(n))=1(1-(1)/(n))+(1-(1)/(n))^(2)+"...."+oo)`
`implies (S)/(n)=(1)/(1-(1-(1)/(n))) " " [S_(oo)=(a)/(1-r) " by GP "]`
`implies S=(n)/((1)/(n))`
`implies S=n^(2)`.


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