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The expression `sum_(n=1)^(oo)cot^(-1)(n^(2)-3n+3)` simplifies toA. `(pi)/(4)`B. `(pi)/(2)`C. `(3pi)/(4)`D. `pi` |
Answer» Correct Answer - C `S=sum_(n=1)^(oo)cos^(-1)(n^(2)-3n+3)` `=sum_(n=1)^(oo)tan^(-1)((1)/(1+n^(2)-3n+2))` `=sum_(n=1)^(oo)tan^(-1)(((n-1)-(n-2))/(1+(n-1)(n-2)))` `=sum_(n=1)^(oo)(tan^(-1)(n-1)-tan^(-1)(n-2))` `=(pi)/(2)+(pi)/(4)=(3pi)/(4)` |
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