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In mathematics, Abel's theorem for power series relates a limit of a power series to the sum of its coefficients. It is named after Norwegian mathematician Niels Henrik Abel. ==Theorem== Let ''a'' = be any sequence of real or complex numbers and let : be the power series with coefficients ''a''. Suppose that the series converges. Then : where the variable ''z'' is supposed to be real, or, more generally, to lie within any ''Stolz angle'', that is, a region of the open unit disk where : for some ''M''. Without this restriction, the limit may fail to exist: for example, the power series : converges to 0 at ''z'' = 1, but is unbounded near any point of the form ''e''i/3''n'', so the value at ''z'' = 1 is not the limit as ''z'' tends to 1 in the whole open disk. Note that is continuous on the real closed interval (''t'' ) for ''t'' < 1, by virtue of the uniform convergence of the series on compact subsets of the disk of convergence. Abel's theorem allows us to say more, namely that is continuous on (). 抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』 ■ウィキペディアで「Abel's theorem」の詳細全文を読む スポンサード リンク
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