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Sum of series cos(x)^2



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The solution

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  oo         
 ___         
 \  `        
  \      2   
  /   cos (x)
 /__,        
n = 1        
$$\sum_{n=1}^{\infty} \cos^{2}{\left(x \right)}$$
Sum(cos(x)^2, (n, 1, oo))
The radius of convergence of the power series
Given number:
$$\cos^{2}{\left(x \right)}$$
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
$$a_{n} = \cos^{2}{\left(x \right)}$$
and
$$x_{0} = 0$$
,
$$d = 0$$
,
$$c = 1$$
then
$$1 = \lim_{n \to \infty} 1$$
Let's take the limit
we find
True

False
The answer [src]
      2   
oo*cos (x)
$$\infty \cos^{2}{\left(x \right)}$$
oo*cos(x)^2

    Examples of finding the sum of a series