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question 9 of 13 > let $a_{n}=\frac{n^{2}}{n^{4}-5}$ and $b_{n}=\frac{1}{n^{2}}$. calculate the following limit. $lim_{n \to infty}\frac{a_{n}}{b_{n}}$ (give an exact answer. use symbolic notation and fractions where needed. enter dne if the limit does not exist.) $lim_{n \to infty}\frac{a_{n}}{b_{n}}=$ determine the convergence of $sum_{n = 1}^{infty}a_{n}$. $sum_{n = 1}^{infty}a_{n}$ diverges by the limit comparison test because $sum_{n = 1}^{infty}b_{n}$ diverges and $lim_{n \to infty}\frac{a_{n}}{b_{n}}$ is infinite. $sum_{n = 1}^{infty}a_{n}$ converges by the limit comparison test because $sum_{n = 1}^{infty}b_{n}$ converges and $lim_{n \to infty}\frac{a_{n}}{b_{n}}$ exists and is finite. $sum_{n = 1}^{infty}a_{n}$ converges by the limit comparison test because $sum_{n = 1}^{infty}b_{n}$ converges and $lim_{n \to infty}\frac{a_{n}}{b_{n}}$ does not exist. $sum_{n = 1}^{infty}a_{n}$ diverges by the limit comparison test because $sum_{n = 1}^{infty}b_{n}$ diverges.
Step1: Substitute \(a_n\) and \(b_n\) into the limit.
We have \(\lim_{n
ightarrow\infty}\frac{a_n}{b_n}=\lim_{n
ightarrow\infty}\frac{\frac{n^2}{n^4 - 5}}{\frac{1}{n^2}}\). When dividing by a fraction, we multiply by its reciprocal, so \(\lim_{n
ightarrow\infty}\frac{n^2}{n^4 - 5}\times n^2=\lim_{n
ightarrow\infty}\frac{n^4}{n^4 - 5}\).
Step2: Divide numerator and denominator by \(n^4\).
\(\lim_{n
ightarrow\infty}\frac{n^4}{n^4 - 5}=\lim_{n
ightarrow\infty}\frac{\frac{n^4}{n^4}}{\frac{n^4}{n^4}-\frac{5}{n^4}}=\lim_{n
ightarrow\infty}\frac{1}{1 - \frac{5}{n^4}}\).
Step3: Evaluate the limit as \(n
ightarrow\infty\).
As \(n
ightarrow\infty\), \(\frac{5}{n^4}
ightarrow0\). So \(\lim_{n
ightarrow\infty}\frac{1}{1 - \frac{5}{n^4}}=\frac{1}{1-0}=1\).
For the convergence of \(\sum_{n = 1}^{\infty}a_n\), we know that the \(p -\) series \(\sum_{n=1}^{\infty}b_n=\sum_{n = 1}^{\infty}\frac{1}{n^2}\) is a \(p -\) series with \(p = 2>1\), so \(\sum_{n=1}^{\infty}b_n\) converges. Since \(\lim_{n
ightarrow\infty}\frac{a_n}{b_n}=1\) (a positive - finite number), by the Limit Comparison Test, \(\sum_{n = 1}^{\infty}a_n\) converges.
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\(\lim_{n
ightarrow\infty}\frac{a_n}{b_n}=1\)
\(\sum_{n = 1}^{\infty}a_n\) converges by the Limit Comparison Test because \(\sum_{n = 1}^{\infty}b_n\) converges and \(\lim_{n
ightarrow\infty}\frac{a_n}{b_n}\) exists and is finite.