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Sum of series exp(-nx)



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The solution

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  oo       
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  \    -n*x
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n = 0      
$$\sum_{n=0}^{\infty} e^{- n x}$$
Sum(exp((-n)*x), (n, 0, oo))
The radius of convergence of the power series
Given number:
$$e^{- n x}$$
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
$$a_{n} = e^{- n x}$$
and
$$x_{0} = 0$$
,
$$d = 0$$
,
$$c = 1$$
then
$$1 = \lim_{n \to \infty}\left(e^{- n \operatorname{re}{\left(x\right)}} e^{\left(n + 1\right) \operatorname{re}{\left(x\right)}}\right)$$
Let's take the limit
we find
$$1 = e^{\operatorname{re}{\left(x\right)}}$$
False
The answer [src]
  oo       
 ___       
 \  `      
  \    -n*x
  /   e    
 /__,      
n = 0      
$$\sum_{n=0}^{\infty} e^{- n x}$$
Sum(exp(-n*x), (n, 0, oo))

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