- #1
fmam3
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Homework Statement
Suppose the series [tex]\sum_{n=0}^{\infty} a_n x^n[/tex] has radius of convergence [tex]R[/tex] and converges at [tex]x = R[/tex]. Prove that [tex]\lim_{x \to R^{-}}\large( \sum_{n = 0}^{\infty} a_n x^n \large) = \sum_{n = 0}^{\infty} \large( \lim_{x \to R^{-}} a_n x^n \large) [/tex]
2. Question
For the case [tex]R \in \mathbb{R}-\{0\}[/tex] (i.e. the radius of convergence is a finite nonzero real number), then the above is a straight forward application of Abel's Theorem on the LHS, and an easy application of the fact that [tex]x^n[/tex] is a continuous function on [tex]\mathbb{R}[/tex] on the RHS. If [tex]R = 0[/tex], then the result is trivial.
However, my question is how do you (or do you even) deal with the case [tex]R = \pm \infty[/tex]? That is, do we even say that the power series converges at [tex]x = R = \pm \infty[/tex]?
Thanks in advance!