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If the coefficient of `x^(n)` in `(1+x)^(101) (1+x^(3)-x^(6))^(30)` isA. `3r+1`B. `3r`C. `3r+2`D. none of these |
Answer» Correct Answer - C We havec `(1+x)^(101)(1-x+x^(2))^(100)` `= (1+x)((1+x)(1-x+x^(2)))^(100)` `= (1+x)(1+x^(3))^(100)` `= (1+x){C_(0) + C_(1)x^(3)+C_(2)x^(6)+"…."+C_(100)x^(300)}`, where `C_(r) = .^(100)C_(r)` `= (1+x)underset(r=0)overset(n)sum.^(n)C_(r)x^(3r)=underset(r=0)overset(n)sum.^(n)C_(r)x^(3r)+underset(r=0)overset(n)sum.^(n)C_(r)x^(3r+1)` Hence, there will be no term containing `3r+2`. |
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