A) 56
B) 55
C) 45
D) 15
Correct Answer: B
Solution :
\[{{x}^{7}}\],\[{{x}^{8}}\]will occur in \[{{T}_{8}}\]and\[{{T}_{9}}\]. Coefficients of \[{{T}_{8}}\] and \[{{T}_{9}}\]are equal. \[\therefore {{\,}^{n}}{{C}_{7}}{{2}^{n-7}}{{\left( \frac{1}{3} \right)}^{7}}={{\,}^{n}}{{C}_{8}}{{2}^{n-8}}{{\left( \frac{1}{3} \right)}^{8}}\,\,\Rightarrow n=55\].You need to login to perform this action.
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