Geometric Series Test Rather Than Integral Test

In summary, the given series can be rewritten as a geometric series with a common ratio of 1/2. There is no need for manipulation, as n can start at any value. However, if n must start at 0, the series can be adjusted by factoring out 1/2 and changing the index, or by adding 1 to the series and subtracting 1 from the result.
  • #1
Bashyboy
1,421
5

Homework Statement


[itex]\sum_{n=1}^{\infty} \frac{1}{2^n}[/itex]


Homework Equations





The Attempt at a Solution


Could I some how manipulate this to fit a geometric series, so that I may instead use the geometric series test?
 
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  • #2
[tex]\frac{1}{2^n}= \left(\frac{1}{2}\right)^n[/tex]
 
  • #3
Bashyboy said:

Homework Statement


[itex]\sum_{n=1}^{\infty} \frac{1}{2^n}[/itex]

Homework Equations



The Attempt at a Solution


Could I some how manipulate this to fit a geometric series, so that I may instead use the geometric series test?
Hint:

No manipulation is required.
 
  • #4
Well, I was told by my teacher that n couldn't equal one for the geometric series to be implemented, was he, perhaps, wrong?
 
  • #5
Bashyboy said:
Well, I was told by my teacher that n couldn't equal one for the geometric series to be implemented, was he, perhaps, wrong?
Do you mean, n can't start at 1, it must start at zero?

If so factor 1/2 out of your series & change the index accordingly,

else,

Add 1 to your series so that it starts at n=0, and subtract 1 from your result.
 

What is the Geometric Series Test?

The Geometric Series Test is a method used to determine the convergence or divergence of a geometric series. It involves calculating the common ratio of the series and using it to determine if the series converges or diverges.

How does the Geometric Series Test differ from the Integral Test?

The Geometric Series Test is based on the comparison of the common ratio to 1, while the Integral Test involves using calculus to evaluate the convergence or divergence of a series. The Geometric Series Test is typically easier to use and requires less mathematical knowledge than the Integral Test.

What is the formula for the Geometric Series Test?

The formula for the Geometric Series Test is:
If |r| < 1, then the geometric series ∑ ar^n converges to a/(1-r).
If |r| ≥ 1, then the geometric series diverges.

Can the Geometric Series Test be used to determine the exact sum of a geometric series?

Yes, if the series converges, the formula for the sum of a geometric series can be used to find the exact sum. The formula is:
S = a / (1-r), where a is the first term and r is the common ratio.

What are the limitations of using the Geometric Series Test?

The Geometric Series Test can only be used on geometric series, which have a constant ratio between consecutive terms. It also only applies to infinite series, not finite series. Additionally, the test may not always be able to determine the convergence or divergence of a series, and in some cases, other methods may need to be used.

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