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(5^n-2^n)/10^n

Sum of series (5^n-2^n)/10^n



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The solution

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  oo         
____         
\   `        
 \     n    n
  \   5  - 2 
   )  -------
  /       n  
 /      10   
/___,        
n = 1        
$$\sum_{n=1}^{\infty} \frac{- 2^{n} + 5^{n}}{10^{n}}$$
Sum((5^n - 2^n)/10^n, (n, 1, oo))
The radius of convergence of the power series
Given number:
$$\frac{- 2^{n} + 5^{n}}{10^{n}}$$
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
$$a_{n} = - 2^{n} + 5^{n}$$
and
$$x_{0} = -10$$
,
$$d = -1$$
,
$$c = 0$$
then
$$\frac{1}{R} = \tilde{\infty} \left(-10 + \lim_{n \to \infty} \left|{\frac{2^{n} - 5^{n}}{2^{n + 1} - 5^{n + 1}}}\right|\right)$$
Let's take the limit
we find
False

False

$$R = 0$$
The rate of convergence of the power series
The answer [src]
3/4
$$\frac{3}{4}$$
3/4
Numerical answer [src]
0.750000000000000000000000000000
0.750000000000000000000000000000
The graph
Sum of series (5^n-2^n)/10^n

    Examples of finding the sum of a series