Cauchy-hadamard theorem

Question

Assignment:

Cauchy- Hadamard Theorem :-                                   
For every power series  ∑^∞_n=0 a_nzⁿ there exist a number R ,  0≤R≤∞ called the radius of convergence with the following properties:
  
(i) The series converges absolutely for every |z|(ii) If 0≤ρ(iii) If |z|>R, the terms of the series are unbounded and the series is consequently divergent.

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