The sum to infinite terms of the series cosec−1√10+cosec−1√50+cosec−1√170+......+cosec−1√(n2+1)(n2+2n+2) is
A
π4
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B
π2
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C
π3
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D
π6
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Solution
The correct option is Aπ4 Given series =cot−1(3)+cot−1(7)+cot−1(13)+cot−1(21)+....=Tan−1(13)+Tan−1(17)+Tan−1(113)+Tan−1(121)+.....=∑∞n=1Tan−1(11+n(n+1))=π4