Comparison Test problem with infinite series

In summary, the problem is to determine the convergence of the series ∑ sin(1/n^2) from 1 to ∞, and the student was struggling to apply the Comparison Test and Limit Comparison Test. After some guidance, they were able to correctly compare the series with 1/n^2 and determine that it converges.
  • #1
TheRascalKing
7
0

Homework Statement


I need to use the Comparison Test or the Limit Comparison Test to determine whether or not this series converges:

∑ sin(1/n^2) from 1 to ∞


Homework Equations



Limit Comparison Test: Let {An} and {Bn} be positive sequences. Assume the following limit exists:
L = lim[n→∞] An/Bn
if L>0, then ƩAn converges iff ƩBn converges.
if L = ∞ and ƩAn converges, then ƩBn converges.
if L = 0 and ƩBn converges, then ƩAn converges.

Comparison Test: Assume that there exists M > 0 such that 0 ≤ An ≤ Bn for n ≥ M.
if Ʃ[n=1 to ∞] Bn converges, then Ʃ[n=1 to ∞]An also converges.
if Ʃ[n=1 to ∞] An diverges, then Ʃ[n=1 to ∞]Bn also diverges.

The Attempt at a Solution



I've tried comparing with sin(1/n), sin(n), sin(1/n^3), sin(1/n^4), and a handful of other functions involving sin.

Sorry, I'm new to the comparison test and limit comparison test :/
 
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  • #2
TheRascalKing said:

Homework Statement


I need to use the Comparison Test or the Limit Comparison Test to determine whether or not this series converges:

∑ sin(1/n^2) from 1 to ∞


Homework Equations



Limit Comparison Test: Let {An} and {Bn} be positive sequences. Assume the following limit exists:
L = lim[n→∞] An/Bn
if L>0, then ƩAn converges iff ƩBn converges.
if L = ∞ and ƩAn converges, then ƩBn converges.
if L = 0 and ƩBn converges, then ƩAn converges.

Comparison Test: Assume that there exists M > 0 such that 0 ≤ An ≤ Bn for n ≥ M.
if Ʃ[n=1 to ∞] Bn converges, then Ʃ[n=1 to ∞]An also converges.
if Ʃ[n=1 to ∞] An diverges, then Ʃ[n=1 to ∞]Bn also diverges.

The Attempt at a Solution



I've tried comparing with sin(1/n), sin(n), sin(1/n^3), sin(1/n^4), and a handful of other functions involving sin.

Sorry, I'm new to the comparison test and limit comparison test :/

Try comparing with 1/n^2. You know that converges, yes?
 
  • #3
Thanks, got it now. I was using the Limit Comparison test wrong >.<
 

Related to Comparison Test problem with infinite series

1. What is the Comparison Test method for infinite series?

The Comparison Test method is used to determine the convergence or divergence of an infinite series by comparing it to another known series. It states that if the terms of a given series are always less than or equal to the terms of a convergent series, then the given series must also converge. If the terms are always greater than or equal to the terms of a divergent series, then the given series must also diverge.

2. How do you use the Comparison Test to determine convergence or divergence?

To use the Comparison Test, you must first identify a known series with either known convergence or divergence. Then, compare the terms of the given series to the terms of the known series. If the terms of the given series are always less than or equal to the terms of the known convergent series, then the given series must also converge. If the terms of the given series are always greater than or equal to the terms of the known divergent series, then the given series must also diverge.

3. What are some common known series used in the Comparison Test?

Some common known series used in the Comparison Test include the p-series, geometric series, and harmonic series. These series have well-known convergence or divergence properties, making them useful for comparison.

4. Can the Comparison Test be used for all infinite series?

No, the Comparison Test can only be used for series with positive terms. It also cannot be used for alternating series or series with non-constant terms.

5. Are there any limitations to the Comparison Test method?

Yes, there are some limitations to the Comparison Test method. It can only determine convergence or divergence, not the actual value of the series. It also requires the existence of a known series for comparison, which may not always be available.

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