1.

Let `f(n)= (k=1)Σ^n k^2(n C_k)^ 2` then the value of f(5) equalsA. `1000`B. `1250`C. `1750`D. `2500`

Answer» Correct Answer - C
`(c )` `k^(n)C_(k)=n^(n-1)C_(k-1)`
`:.sum_(k=1)^(n)k^(2)("^(n)C_(k))^(2)`
`=n^(2)sum_(k=1)^(n)("^(n-1)C_(k-1))^(2)`
`=n^(2)("^(2n-2)C_(n-1))`
`:. F(5)=25("^(8)C_(4))=1750`


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