A) - 56
B) 56
C) - 14
D) 14
Correct Answer: C
Solution :
\[(8-r)(2)+r(-1)=7\Rightarrow 16-2r-r=7\Rightarrow r=3\] Thus coefficient of x7 is \[={{\,}^{8}}{{C}_{3}}{{\left( \frac{1}{2} \right)}^{5}}{{(-2)}^{3}}=-\frac{8\times 7\times 6}{3\times 2\times 1}\times \frac{1}{4}=-14\].You need to login to perform this action.
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