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[parent] termwise differentiation (Theorem)
Theorem 1   If in the open interval $ I$, all the terms of the series
$\displaystyle f_1(x)\!+\!f_2(x)\!+\cdots$ (1)

have continuous derivatives, the series converges having sum $ S(x)$ and the differentiated series $ f_1'(x)\!+\!f_2'(x)\!+\!\cdots$ converges uniformly on the interval $ I$, then the series (1) can be differentiated termwise, i.e. in every point of $ I$ the sum function $ S(x)$ is differentiable and
$\displaystyle \frac{d\,S(x)}{dx} = f_1'(x)\!+\!f_2'(x)\!+\cdots$
The situation implies also that the series (1) converges uniformly on $ I$.



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See Also: power series

Other names:  differentiating a series
Keywords:  uniform convergence

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Cross-references: converges uniformly, implies, differentiable, sum function, point, interval, sum, converges, derivatives, continuous, series, open interval
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This is version 6 of termwise differentiation, born on 2004-09-25, modified 2006-09-24.
Object id is 6231, canonical name is TermwiseDifferentiation.
Accessed 3612 times total.

Classification:
AMS MSC40A30 (Sequences, series, summability :: Convergence and divergence of infinite limiting processes :: Convergence and divergence of series and sequences of functions)
 26A15 (Real functions :: Functions of one variable :: Continuity and related questions )

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