Sum of series 0.4^n

The solution

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  oo      
 ___      
 \  `     
  \      n
  /   2/5 
 /__,     
n = 1

$$\sum_{n=1}^{\infty} \left(\frac{2}{5}\right)^{n}$$

Sum((2/5)^n, (n, 1, oo))

The radius of convergence of the power series

Given number:
$$\left(\frac{2}{5}\right)^{n}$$
It is a series of species
$$a_{n} \left(c x - x_{0}\right)^{d n}$$
- power series.
The radius of convergence of a power series can be calculated by the formula:
$$R^{d} = \frac{x_{0} + \lim_{n \to \infty} \left|{\frac{a_{n}}{a_{n + 1}}}\right|}{c}$$
In this case
$$a_{n} = 1$$
and
$$x_{0} = - \frac{2}{5}$$
,
$$d = 1$$
,
$$c = 0$$
then

False

Let's take the limit
we find

False

The rate of convergence of the power series

The answer [src]

2/3

$$\frac{2}{3}$$

2/3

Numerical answer [src]

0.666666666666666666666666666667

0.666666666666666666666666666667

The graph

Examples of finding the sum of a series

The Sum of the Power Series
```
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```
```
(x-1)^n
```
Factorial
```
1/2^(n!)
```
```
n^2/n!
```
```
x^n/n!
```
```
k!/(n!*(n+k)!)
```
Flint Hills Series
```
csc(n)^2/n^3
```
Basel problem
```
1/n^2
```
```
1/n^4
```
```
1/n^6
```
Harmonic series
```
1/n
```
Grandi's series
```
(-1)^n
```
Alternating series
```
(-1)^(n + 1)/n
```
```
(n + 2)*(-1)^(n - 1)
```
```
(3*n - 1)/(-5)^n
```
```
(-1)^(n - 1)*n/(6*n - 5)
```
Newton–Mercator series
```
(-1)^(n + 1)/n*x^n
```
Exam the series for convergence
```
(3*n - 1)/(-5)^n
```

Other calculators

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Identical expressions

Sum of series 0.4^n

The solution

Examples of finding the sum of a series