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The coefficients of `x^(13)` in the expansion of ` (1 - x)^(5) (1 + x + x^(2) + x^(3) )^(4)` , isA. 4B. -4C. 9D. none of these |
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Answer» Correct Answer - a We have, `(1- x)^(5) (1 + x + x^(2) + x^(3) )^(4)` `= (1 x)^(5) (1 | x)^(4) (1 | x^(2))^(4)` ` = (1 - x) (1 - x^(2))^(4) (1 + x^(2))^(4)` ` = (1 -x )(1 - x^(4))^(4)` ` = (1 - x) (""^(4)C_(0) - ""^(4)C_(1)x^(4) + ""^(4)C_(2) x^(8) - ""^(4)C_(3)x^(12) + ""^(4)C_(4) x^(16))` `therefore ` Coefficient of ` x^(13) = ""^(4)C_(3) = 4` . |
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