A) - 455
B) - 105
C) 105
D) 455
Correct Answer: A
Solution :
\[{{T}_{r+1}}=\,{}^{15}{{C}_{r}}{{({{x}^{4}})}^{15-r}}{{(-1/{{x}^{3}})}^{r}}\]= \[{{(-1)}^{r}}\,\,{}^{15}{{C}_{r}}{{(x)}^{60-7r}}\] For coefficient of\[{{x}^{39}}\], \[60-7r=39\Rightarrow r=3\] \ \[{{T}_{4}}={}^{15}{{C}_{3}}{{({{x}^{4}})}^{12}}{{(-1/{{x}^{3}})}^{3}}\]= \[-455\,{{x}^{39}}\] Hence the required coefficient is - 455.You need to login to perform this action.
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