Gujarati
7.Binomial Theorem
hard

$(1+x)\left(1+x^2\right)\left(1+x^3\right) \ldots\left(1+x^{100}\right)$ के विस्तार में $x^9$ के गुणांक का मान है

A

$6$

B

$7$

C

$8$

D

$9$

(IIT-2015)

Solution

$x^9$ can be formed in $8$ ways

i.e. $x ^9, x ^{1+8}, x ^{2+7}, x ^{3+6}, x ^{4+5}, x ^{1+2+6}, x ^{1+3+5}, x ^{2+3+4}$ and coefficient in each case is $1$ $\Rightarrow$ Coefficient of $x^9=1+1+1+\ldots \ldots \ldots+1=8$

Standard 11
Mathematics

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