1.

The value of `""(n)C_(1). X(1 - x )^(n-1) + 2 . ""^(n)C_(2) x^(2) (1 - x)^(n-2)` ` + 3. ""^(n)C_(3) x^(3) (1 - x)^(n-3) + ….+ n ""^(n)C_(n) x^(n) , n in ` N isA. nxB. ` n(n -x)`C. ` n (x-1)`D. none of these

Answer» Correct Answer - a
We have,
` ""^(n)C_(1) . X(1 - x)^(n-1) + 2. ""^(n)C_(2) x^(2) (1 - x)^(n-2)`
`+ 3. ""^(n)C_(3) x^(3) (1 -x)^(n-3) + …+ n ""^(n)C_(n) x^(n)`
` = sum_(r=1)^(n) r. ""^(n)C_(r)(1 - x)^(n-r)`
` = sum_(r=1)^(n) r. ""^(n-1)C_(r-1)x^(r) (1 - x)^(n-r)`
` =nx sum_(r=1)^(n) ""^(n-1)C_(r-1)x^(r-1) (1 - x)^((n-1 )-(r-1))`
` nx (x + 1 - x )^(n-1)= nx ` .


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