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`sum_(k=1)^(oo) k(1-1/n)^(k-1) =`A. `n(n-1)`B. `n(n+1)`C. `n^(2)`D. `(n+1)^(2)` |
Answer» Correct Answer - C `underset(k=1)overset(oo)sumk(1-1/n)^(k=1)` `=1-2(1-(1)/(n))^(1)+3(1+1/n)^(2)+"….."` `= 1+2r+3t^(2)+"…"` `= (1-t)^(-2)` `= [1-(1-(1)/(n))]^(-2) = (1/n)^(-2) = n^(2)` |
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