How can the sum of a geometric series be evaluated?

In summary, the person is asking for help evaluating the sum of a series from 1 to infinity, which is represented by (-1)^{n-1}*(\frac{4^n}{7^n}). They know the answer is 4/11 but do not know how to get it. They are then directed to look at the series as a geometrical series and use the formula \frac{a}{1-r} to find the sum.
  • #1
thenewbosco
187
0
i have the following series from 1 to infinity:
[tex]\sum(-1)^{n-1}*(\frac{4^n}{7^n})[/tex]
how can i evaluate the sum of this?
thanks
i know the answer is 4/11 but i do not know how to get this.
 
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  • #2
Look closer; it's just a geometrical serie.

What you might have missed: [itex](-1)^{n-1}=(-1)^{n+1}[/itex].
 
  • #3
how does this fact help me find what the sum is equal to?
 
  • #5
It's like quasar said you need to rewrite into the form

[tex] \sum_{n=0}^{\infty} ar^n = \frac{a}{1-r}[/tex]

where

[tex] a \neq 0 [/tex]
 

FAQ: How can the sum of a geometric series be evaluated?

What is the definition of convergence of a series?

The convergence of a series refers to the behavior of the terms in the series as the number of terms increases towards infinity. A series is said to be convergent if the sum of its terms approaches a finite value. This means that as more terms are added to the series, the sum of those terms gets closer and closer to a specific value.

How do you determine if a series is convergent or divergent?

To determine if a series is convergent or divergent, one can use various tests such as the comparison test, ratio test, or root test. These tests compare the given series to a known series that is either convergent or divergent. If the given series has a similar behavior to the known series, then the given series will have the same convergence or divergence as the known series.

What is the difference between absolute convergence and conditional convergence?

A series is absolutely convergent if the absolute values of its terms are convergent. This means that even if the signs of the terms are changed, the series will still converge to the same value. On the other hand, a series is conditionally convergent if the series converges, but the series of absolute values of its terms is divergent. This means that changing the signs of the terms will result in a different sum for the series.

Can a series be both convergent and divergent?

No, a series cannot be both convergent and divergent. A series can only have one of these two behaviors. If the terms of the series approach a finite value, then the series is convergent. If the terms do not approach a finite value, then the series is divergent. It is not possible for a series to have both of these behaviors at the same time.

What is the importance of understanding convergence of series?

Understanding convergence of series is important in many areas of mathematics and science. It allows us to determine whether a given series will approach a finite value or not, which can have practical applications in fields such as physics, engineering, and economics. Additionally, it is a fundamental concept in calculus and is necessary for understanding more advanced topics such as sequences and series, power series, and Taylor series.

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