Solving Geometric Series: 2*(-1/4)^(n-1)

In summary, the given expression can be treated as a geometric series with A = 2 and r = -1/4, and the series converges and its sum can be determined by using the formula for a geometric series.
  • #1
mattmannmf
172
0
{sigma} 2*(-1/4)^(n-1)

Could i treat this as a geometric series? i know geometric is in the form of ar^n but the n is (n-1)

my A=2
my r= -1/4
 
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  • #2
Your series appears to be
[tex]\sum_{n = 1}^{\infty} 2 (-1/4)^{n - 1}[/tex]

Write a few terms of this series and see if you can adjust the starting index.
 
  • #3
i have no idea what you mean by that
 
  • #4
mattmannmf said:
{sigma} 2*(-1/4)^(n-1)

Could i treat this as a geometric series? i know geometric is in the form of ar^n but the n is (n-1)

my A=2
my r= -1/4

You have
2(-1/4)n-1
and you want
A rn-1
?

Why not set them equal and try solving for A and r?
 
  • #5
no... I am trying to solve whether or not the series converges or diverges and then i have to determine the sum of the series... meaning where the series sums up to..
 
  • #6
Oh, my mistake. I thought the method you had wanted to use was to rewrite the summand in a standard form, and were stuck on how to do that rewrite.
 
  • #7
Well, just change n-1 into n using exponent rules.
 
  • #8
Write a few terms of the series and you should quickly see that it is a geometric series. A geometric series is one for which each term is a constant multiple of the previous term.
 

Related to Solving Geometric Series: 2*(-1/4)^(n-1)

1. What is a geometric series?

A geometric series is a series of numbers where each term is found by multiplying the previous term by a constant value. For example, in the series 2, 6, 18, 54, ... the constant value is 3.

2. How do you solve a geometric series?

To solve a geometric series, you can use the formula: Sn = a(1-r^n)/(1-r), where Sn is the sum of the first n terms, a is the first term, and r is the common ratio between terms. You can also use the formula for the sum of an infinite geometric series, which is Sn = a/(1-r).

3. What does the expression 2*(-1/4)^(n-1) represent in a geometric series?

The expression 2*(-1/4)^(n-1) represents the general term in a geometric series where the first term is 2 and the common ratio is -1/4. This means that each term is found by multiplying the previous term by -1/4.

4. How do you find the sum of a geometric series using the given expression?

To find the sum of a geometric series using the expression 2*(-1/4)^(n-1), you would substitute the values of a=2 and r=-1/4 into the formula Sn = a/(1-r). This would give you the sum of the first n terms in the series.

5. Can a geometric series have a negative common ratio?

Yes, a geometric series can have a negative common ratio. This will result in alternating positive and negative terms in the series. However, the series will only converge (have a finite sum) if the absolute value of the common ratio is less than 1.

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