A) \[5\]
B) \[7\]
C) \[6\]
D) \[4\]
Correct Answer: B
Solution :
Given that, \[{{T}_{n+1}}-{{T}_{n}}=21\] \[\therefore \] \[^{n+1}{{C}_{3}}{{-}^{n=21}}{{C}_{3}}\] \[\Rightarrow \] \[n(n-1)\,\left( \frac{3}{6} \right)=21\] \[\Rightarrow \] \[n(n-1)=42\,\,\Rightarrow \,\,n=7\]You need to login to perform this action.
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