How to Use Absolute Convergence Test on This Series?

In summary: So it is not a concern in finding the radius of convergence. In summary, the given series is being tested for absolute convergence using the limit comparison test. The radius of convergence for the given function is 1, as determined by the ratio test. The exponent $k$ in the summand is not a concern when finding the radius of convergence.
  • #1
karush
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$$\sum_{k=1}^{\infty}\left(\frac{k}{k+1}\right)^{2k}$$
$\textsf{how do you use absolute converge test on this?}$
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  • #2
I think what I would do here is compute:

\(\displaystyle L=\lim_{k\to\infty}\left(\left(\frac{k}{k+1}\right)^{2k}\right)\)

If $L\ne0$, then the series must diverge. Bear in mind though, that this test is inconclusive if the limit of the summand is zero.
 
  • #3
$\textsf{Find the radius / interval of convergence }\\$
\begin{align}
\displaystyle f(x)&=2k(x-1)^k
\end{align}
$\textsf{thot would ask another questions here since new stuff?}$
 
  • #4
karush said:
$\textsf{Find the radius / interval of convergence }\\$
\begin{align}
\displaystyle f(x)&=2k(x-1)^k
\end{align}
$\textsf{thot would ask another questions here since new stuff?}$

If we are given:

\(\displaystyle f(x)=\sum_{k=0}^{\infty}\left(2k(x-1)^k\right)\)

Then we compute the radius of convergence as follow:

\(\displaystyle |x-1|<\lim_{k\to\infty}\left|\frac{2k}{2(k+1)}\right|=1\)
 
  • #5
MarkFL said:
If we are given:

\(\displaystyle f(x)=\sum_{k=0}^{\infty}\left(2k(x-1)^k\right)\)

Then we compute the radius of convergence as follow:

\(\displaystyle |x-1|<\lim_{k\to\infty}\left|\frac{2k}{2(k+1)}\right|=1\)

$\text{what happened to the exponent $k$ or that a concern?}$
 
  • #6
We are only concerned with the coefficient of the exponential term. In fact we can even remove any constant factors in that coefficient.
 

FAQ: How to Use Absolute Convergence Test on This Series?

What is the "Use absolute converge test"?

The absolute converge test is a method used to determine if a series converges or diverges. It involves taking the absolute value of each term in the series and then testing if the resulting series converges or diverges.

When should the absolute converge test be used?

The absolute converge test should be used when the terms in a series alternate in sign or when the series contains only positive terms. In these cases, the absolute value of the terms can help determine the convergence or divergence of the series.

How does the absolute converge test work?

The absolute converge test works by taking the absolute value of each term in a series and then comparing the resulting series to known series that either converge or diverge. If the resulting series is similar to a convergent series, then the original series also converges. If the resulting series is similar to a divergent series, then the original series also diverges.

What are the advantages of using the absolute converge test?

The absolute converge test can be useful in determining the convergence or divergence of a series when other tests, such as the ratio or root tests, are inconclusive. It can also be used to simplify a series by removing alternating signs or negative terms.

Are there any limitations to the absolute converge test?

Yes, the absolute converge test is not always conclusive and may give incorrect results for certain types of series. It should always be used in conjunction with other tests to confirm the convergence or divergence of a series.

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