Summation of a Logarithmic Series

In summary, the sum of the given series is log(200/2), or simply log(100). This is because all terms in the series, except for 1/2 and 200/1, cancel out, leaving only those two terms. Thus, the sum can be simplified to log(200/2), which is equivalent to log(100) since 200/2 = 100.
  • #1
S.R
81
0

Homework Statement


What is the sum of the following series?

log(3/2)+log(4/3)+log(5/4)+...log(200/199).

Where log(x) is log base 10 of x.

Homework Equations





The Attempt at a Solution


Evidently, the previous form equals:

log(3/2*4/3*5/4*...200/199)

I'm missing something - no patterns are evident to me other than the denominator and numerator of the subsequent terms cancel out.

Any guidance would be appreciated.
 
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  • #2
S.R said:
I'm missing something - no patterns are evident to me other than the denominator and numerator of the subsequent terms cancel out.

And that's important! What are you left with after cancelling *everything* that can be cancelled?
 
  • #3
[tex]log(\frac{3}{2}*\frac{4}{3}*\frac{5}{4}*\frac{6}{5}...*\frac{200}{199})[/tex]

Do you see in what pattern the terms cancel and which terms are left? :wink:
 
  • #4
Intuitively, yes - would it be correct in saying that all terms cancel other than 1/2 and 200/1, leaving 200/2?
 
  • #5
S.R said:
Intuitively no - however, would it be correct in saying that all terms cancel other than 1/2 and 200/1, leaving 200/2?
Yes, that would be correct, and you didn't find it intuitive even though you spotted the pattern?
 
  • #6
S.R said:
Intuitively no - however, would it be correct in saying that all terms cancel other than 1/2 and 200/1, leaving 200/2?

Yes, only 1/2 and 200/1 remains. 3 cancels 1/3, 4 cancels 1/4, 5 cancels 1/5 but there's no one to cancel 200 and 1/2.
 
  • #7
Quickly edited after rereading :frown:. I'm not sure why I didn't recognize that pattern before.
 

1. What is a logarithmic series?

A logarithmic series is a series in which the terms increase or decrease logarithmically, meaning that each term is a multiple of the previous term raised to a power. The most common example of a logarithmic series is the harmonic series, where the terms decrease logarithmically.

2. How do you find the sum of a logarithmic series?

The sum of a logarithmic series can be found by using the formula S = a/(1-r), where S is the sum, a is the first term, and r is the common ratio between consecutive terms. This formula only applies if the absolute value of r is less than 1, otherwise the series diverges.

3. What is the convergence of a logarithmic series?

A logarithmic series converges if the absolute value of the common ratio between consecutive terms is less than 1. If the absolute value of the common ratio is greater than or equal to 1, the series diverges.

4. Can a logarithmic series have a negative common ratio?

Yes, a logarithmic series can have a negative common ratio. This means that the terms of the series will alternate between positive and negative values.

5. What is the practical application of the summation of a logarithmic series?

The summation of a logarithmic series has various applications in mathematics and physics, such as in the calculation of infinite sums, the estimation of integrals, and the prediction of population growth in certain models. It also has applications in finance, particularly in the calculation of compound interest over time.

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