Q117 / 180 · COMEDK 2018 · Mathematics
$\lim _{n \rightarrow \infty} \frac{\left(1^{2}+2^{2}+\ldots+n^{2}\right) \sqrt[n]{n}}{(n+1)(n+10)(n+100)}=$
- A3
- Correct answerB$\frac{1}{3}$
- C$\frac{2}{3}$
- D$\infty$
Solution
We have,
$$
\begin{aligned}
\lim _{n \rightarrow \infty} \frac{\left(1^{2}+2^{2}+\ldots+n^{2}\right) \sqrt[n]{n}}{(n+1)(n+10)(n+100)} \\
=& \lim _{n \rightarrow \infty} \frac{n(n+1)(2 n+n)}{6(n+1)(n+10)(n+100)}\left(\lim _{n \rightarrow \infty} \sqrt[n]{n}\right) \\
=& \lim _{n \rightarrow \infty} \frac{2 n^{2}+n}{6(n+10)(n+100)} \\
=& \lim _{n \rightarrow \infty} \frac{2+\frac{1}{n}}{6\left(1+\frac{10}{n}\right)\left(1+\frac{100}{n}\right)} \\
=& \frac{2+0}{6(1+0)(1+0)} \\
=& \frac{2}{6}=\frac{1}{3}
\end{aligned}
$$
Hence, the correct answer is option: 'B'.