Advanced Calculus Infinite Series

In summary, the conversation discusses proving that if a monotone decreasing sequence of positive numbers converges, then the limit of n*a_n must be equal to 0. The approach to the proof involves using the fact that if n*a_n does not converge to 0, then there exists a positive constant e such that n*a_n>e for an infinite number of n, and using the monotonicity to show that a_n must diverge.
  • #1
jtn2007
3
0

Homework Statement



Suppose that {an} is a monotone decreasing sequence of positive numbers. Show that if the series an converges, then the lim(nan)=0.

Homework Equations


The Attempt at a Solution



I started the proof with the fact that since I know the sequence is monotone decreasing and the the series converges then the lim an=0 but I am not sure how to show that the lim nan=o.

any help would be greatly appreciated
 
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  • #2
It's really a lot like the proof the harmonic series diverges. If n*a_n does not converge to 0, then there is a positive constant e such that n*a_n>e for an infinite number of n, right? Use that with the monotonicity to show a_n must diverge.
 

Related to Advanced Calculus Infinite Series

1. What is an infinite series in advanced calculus?

An infinite series is a sum of infinitely many terms. In advanced calculus, we study infinite series where the number of terms approaches infinity. These series can be used to approximate functions and calculate limits.

2. How do you determine if an infinite series converges or diverges?

To determine if an infinite series converges or diverges, we use various tests such as the comparison test, ratio test, or integral test. These tests compare the series to a known convergent or divergent series, or use the properties of integrals to determine convergence.

3. Can an infinite series converge to a finite value?

Yes, an infinite series can converge to a finite value. This means that the sum of all the terms in the series approaches a fixed number as the number of terms increases. However, not all infinite series converge, and some may diverge to infinity.

4. What is the difference between absolute and conditional convergence in infinite series?

Absolute convergence refers to when an infinite series converges regardless of the order of its terms. In contrast, conditional convergence means that the rearrangement of the terms can change the sum of the series. In advanced calculus, we often focus on absolute convergence since it is easier to work with.

5. How are infinite series used in real-world applications?

Infinite series are used in various real-world applications such as physics, engineering, and finance. They can be used to model and approximate natural phenomena, calculate probabilities, and solve differential equations. Additionally, infinite series are also used in computer algorithms and compression techniques.

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