Mister Exam

Sum of series arccot(x)



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The solution

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  oo         
 __          
 \ `         
  )   acot(x)
 /_,         
n = 1        
n=1acot(x)\sum_{n=1}^{\infty} \operatorname{acot}{\left(x \right)}
Sum(acot(x), (n, 1, oo))
The radius of convergence of the power series
Given number:
acot(x)\operatorname{acot}{\left(x \right)}
It is a series of species
an(cxx0)dna_{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:
Rd=x0+limnanan+1cR^{d} = \frac{x_{0} + \lim_{n \to \infty} \left|{\frac{a_{n}}{a_{n + 1}}}\right|}{c}
In this case
an=acot(x)a_{n} = \operatorname{acot}{\left(x \right)}
and
x0=0x_{0} = 0
,
d=0d = 0
,
c=1c = 1
then
1=limn11 = \lim_{n \to \infty} 1
Let's take the limit
we find
True

False
The answer [src]
oo*acot(x)
acot(x)\infty \operatorname{acot}{\left(x \right)}
oo*acot(x)

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