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Let `S_(k)=lim_(n to oo) sum_(i=0)^(n) (1)/((k+1)^(i))." Then " sum_(k=1)^(n) kS_(k)` equalsA. `(n(n+1))/(2)`B. `(n(n-1))/(2)`C. `(n(n+2))/(2)`D. `(n(n+3))/(2)` |
Answer» Correct Answer - D We have, `S_(k)=underset(ntooo)limunderset(i=0)overset(n)sum(1)/((k+1)^(i))` `rArr" "S_(k)=1+(1)/((k+1)^(2))+(1)/((k+1)^(3))+ . . . .. ` `rArr" "S_(k)=(1)/(1-(1)/(k+1))=(k+1)/(k)` `:." "underset(k=1)overset(n)sumkS_(k)=underset(k=1)overset(n)sum(k+1)=2+3+ . . . +(n+1)` `rArr" "underset(k=1)overset(n)sumkS_(k)=(n)/(2)(2+n+1)=(n(n+3))/(2)` |
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