Is There an Analytical Solution for This Mathematical Series?

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In summary, the conversation is about finding an analytical result for the series \sum_{k=1} ^t a^{t-k}b^{k-1}. It is determined that the series is actually a polynomial in two variables, with the coefficients all equal to 1. Methods for dealing with the series are discussed, including recognizing familiar patterns and rewriting the series in a simpler form. Ultimately, it is determined that the series can be calculated using the formula \frac{a^{t}-b^{t}}{a-b} with "t" being an uneven number.
  • #1
phonic
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Is it possible to get a analytical result for this series? It looks simple:

[itex]\sum_{k=1} ^t a^{t-k}b^{k-1} [/itex]

Thanks a lot!
 
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  • #2
Hmm.Use [ tex ] & [ /tex ] commands (without the spaces) for opening & closing tex tags.

That's no series,it's a polynomial in 2 variables.

Daniel.
 
  • #3
Thanks for your corection. It's my first time to post message here.

Yes, this is a polynomial, with all coeficient as 1. Is there some method to deal with it?
 
  • #4
Yes,try to write some terms in the sum and then see whether you recognize something familiar.

Daniel.
 
  • #5
Thanks for your hints. I think it can be calculated in this way:
[tex]\sum_{k=1} ^t a^{t-k}b^{k-1} = \frac{a^t}{b}\sum_{k=1} ^t (\frac{b}{a})^{k}[/tex]
 
  • #6
It's easier this way:

[tex] \sum_{k=1}^{t} a^{t-k}b^{k-1}=a^{t-1}b^{0}+a^{t-2}b^{1}+...+a^{1}b^{t-2}+a^{0}b^{t-1}=\frac{a^{t}-b^{t}}{a-b} [/tex]

with "t" uneven.

Daniel.
 

1. How do I calculate the sum of a series?

The sum of a series can be calculated by adding all of the terms in the series together. This can be done manually or by using a formula such as the arithmetic or geometric series formula.

2. What is the difference between an arithmetic and geometric series?

An arithmetic series has a constant difference between each term, while a geometric series has a constant ratio between each term. This means that in an arithmetic series, each term is added or subtracted by a fixed number, while in a geometric series, each term is multiplied or divided by a fixed number.

3. How do I find the nth term in a series?

The nth term in a series can be found by using the formula: an = a1 + (n-1)d for an arithmetic series, or an = a1*r^(n-1) for a geometric series. Here, an represents the nth term, a1 is the first term, d is the common difference in an arithmetic series, and r is the common ratio in a geometric series.

4. What is the limit of a series?

The limit of a series is the value that the sum of the series approaches as the number of terms in the series goes to infinity. This is also known as the convergence of a series. If the limit of a series is a finite number, the series is said to converge, while if the limit is infinity or does not exist, the series is said to diverge.

5. How can I check if a series is convergent or divergent?

There are multiple tests that can be used to determine if a series is convergent or divergent, such as the ratio test, the root test, and the integral test. These tests involve analyzing the behavior of the terms in the series and can help determine if the series will approach a finite limit or not.

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