1.

Coefficient of x^(6) in (1+x)(1+x^(2))^(2)(1+x^(3))^(3)…(1+x^(n))^(n) is

Answer»

`26`
`28`
`30`
`35`

Solution :`(b)` The COEFFICIENT of `X^(6)` in the given expression `=` coefficient of `x^(6)` in
`(1+^(6)C_(1)x^(6))(1+^(5)C_(1)x^(5))(1+^(4)C_(1)x^(4))(1+^(3)C_(1)x^(3)+^(3)C_(2)x^(6))(1+^(2)C_(1)x^(2)+^(2)C_(2)x^(4))(1+x)`
`=` coefficient of `x^(6)` in `(1+6x^(6)+5x^(5)+4x^(4))(1+2x^(2)+3X^(3)+x^(4)+6x^(5)+3x^(6))(1+x)`
`=` coefficient of `x^(6)` in `(11x^(5)+17x^(6))(1+x)=28`


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