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The sum of the series ` sum_(r=0) ^(n) "r."^(2n)C_(r), ` isA. `2^(2n -1) `B. `n . 2^(2n-1)`C. `n 2 ^(n-1)`D. `n 2^(2n - 2)` |
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Answer» Correct Answer - b We have, `sum _(r=0) ^(n) r ""^(2n)C_(r) = sum_(r=0)^(n) r (2n)/(r) ""^(2n -1) C_(r -1)` `sum_(r=0) ^(n) r ""^(2n)C_(r) = n sum_(r=1)^(n) (""^(2n-1)C_(r-1)+""^(2n-1)C_(r-1))` `sum_(r=0)^(n) r ""^(2n)C_(r) = n sum_(r=0)^(n) (""^(2n-1)C_(r-1)+""^(2n - 1) C_(r-1))` `sum_(r=0)^(n) r ""^(2n)C_(r) = n sum_(r=0)^(2n-1) ""^(2n-1)C_(r)= n2^(2n -1)` |
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