1.

The coefficient of `x^(20)` in ` (1 + 3x + 3x^(2) + x^(3))^(20)`,I sA. `""^(60)C_(40)`B. `""^(30)C_(20)`C. `""^(15)C_(2)`D. none of these

Answer» Correct Answer - a
We have ,
`(1 + 3x + 3x^(2) + x^(3))^(20) = { (1+ x)^(3) }^(20) = (1 + x)^(60)`
`therefore ` Coefficient of `x^(20) ` in` (1 + 3x + 3x^(2) + x^(3))^(20)`
= Coefficient of `x^(20)` in `(1 + x)^(60) = ""^(60)C_(20) = ""^(60)C_(40)`


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