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If`C_0,C_1,C_2..C_n` denote the coefficients in the binomial expansion of `(1 +x)^n`, then `C_0 + 2.C_1 +3.C_2+. (n+1) C_n`A. `n2^(n-1)`B. `(n+ 1)2^(n-1)`C. `(n+ 2)2^(n-1)`D. `(n+ 2) 2^(n)` |
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Answer» Correct Answer - c We have, `C_(0) + 2. C_(1) + 3. C_(2) + ... +(n+1) C_(n)` ltbrge `sum _(r=0)^(n) (r + 1) C_(r)` = `sum _(r=0)^(n) (r + 1) ""^(n)C_(r)` `sum _(r=0)^(n) (r .""^(n)C_(r)+ ""^(n)C_(r)) ` `sum _(r=0)^(n) r .""^(n)C_(r)+sum _(r=0)^(n) ""^(n)C_(r)` `sum _(r=0)^(n) r .(n)/(r)""^(n-1)C_(r-1)+sum _(r=0)^(n) ""^(n)C_(r) " "[because ""^(n)C_(r) = (n)/(r). ""^(n-1)C_(r-1) ]` `n(sum_(r=1)^(n) ""^(n-1)C_(r-1))+(sum_(r=1)^(n) ""^(n)C_(r))` ` = n[(""^(n-1)C_(0) + ""^(n-1)C_(1) + ... + ""^(n-1)C_(n-1)]` `+[(""^(n)C_(0) + ""^(n)C_(1) +...+ ""^(n)C_(n))]` `n.2^(n-1)+ 2^(n) = n.2^(n - 1) + 2.2(n-1) = (n +2).2^(n-1)` . |
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