Determine whether the sequence converges or diverges and find the limit

In summary, the problem is asking to determine if the sequence an = 11/n2 = 21/n2 + ... + n1/n2 converges or diverges and to find the limit if it does converge. The solution involves factoring out 1/n^2 and using the formula for (1+2+...+n) in terms of n or alternatively, using a Riemann sum for the function f(x)=x between 0 and 1.
  • #1
Sean1218
86
0

Homework Statement



Determine whether the sequence an = 11/n2 = 21/n2 + ... + n1/n2 converges or diverges. If it converges, find the limit.

2. The attempt at a solution

I have no idea what to do with this problem. I don't see why I can't simplify n/n^2 to 1/n. It was suggested to me to factor out 1/n and introduce the variable i (from Riemann Sums), but I don't see how that helps (and I don't see how I would just introduce i anyway).
 
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  • #2
Factor out the 1/n^2. Can you write an expression for the sum (1+2+...+n)?
 
  • #3
I'm not really sure what you mean.
 
  • #4
Sean1218 said:
I'm not really sure what you mean.

I meant pretty much what I said. an=(1/n^2)*(1+2+...+n), right? Perhaps you know a formula for (1+2+...+n) in terms of n? If not, and you know how to integrate you can also do it as a Riemann sum. Can you write down a Riemann sum for the function f(x)=x between 0 and 1?
 

What is the definition of convergence and divergence?

Convergence and divergence refer to the behavior of a sequence, or a list of numbers, as the number of terms in the sequence approaches infinity. A sequence is said to converge if its terms approach a specific limit as the number of terms increases. On the other hand, a sequence is said to diverge if its terms do not approach a specific limit as the number of terms increases.

How do you determine if a sequence converges or diverges?

To determine if a sequence converges, you need to evaluate the limit of the sequence. This can be done by looking for a pattern in the terms of the sequence or by using mathematical techniques such as the squeeze theorem or the ratio test. If the limit exists and is a finite number, then the sequence converges. If the limit does not exist or is infinite, then the sequence diverges.

What is the significance of finding the limit of a sequence?

Finding the limit of a sequence is important because it helps us understand the long-term behavior of the sequence. It tells us if the terms in the sequence are moving towards a specific value or if they are becoming increasingly erratic. This information can be useful in various fields of science, including physics, biology, and economics.

What are some common types of sequences that frequently converge or diverge?

Some common types of sequences that frequently converge are geometric sequences, where the terms of the sequence are multiplied by a constant factor, and telescoping sequences, where the terms of the sequence cancel each other out. On the other hand, harmonic series, where the terms of the sequence are reciprocals of natural numbers, frequently diverge.

How can knowing the convergence or divergence of a sequence help in solving real-world problems?

In real-world problems, sequences often represent a trend or pattern that is observed over time. Knowing whether the sequence converges or diverges can help in predicting future values and making informed decisions. For example, in economics, knowing the convergence or divergence of a financial series can help in making investment decisions, while in biology, knowing the convergence or divergence of a population growth sequence can help in predicting the future size of a population.

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