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Unformatted text preview: Â§ 11.9 Representations of Functions as Power Series Differention and Integration of Power Series Theorem 2 If the power series âˆ‘ c n ( x a ) n has radius of convergence R > 0, then the function f defined by f ( x ) = c + c 1 ( x a ) + c 2 ( x a ) 2 + Â·Â·Â· = âˆž X n =0 c n ( x a ) n is defferential (and therefore continuous) on the inteval ( a R,a + R ) and (i) f ( x ) = c 1 + 2 c 2 ( x a ) + 3 c 3 ( x a ) 2 + Â·Â·Â· = âˆ‘ âˆž n =1 nc n ( x a ) n 1 (ii) Z f ( d ) dx = C + c ( x a ) + c 1 ( x a ) 2 2 + c 2 ( x a ) 3 3 + Â·Â·Â· = C + âˆž X n =0 c n ( x a ) n +1 n + 1 The radii of convergence of the power series in Equation (i) and (ii) are both R . Note: 1. Equation (i) and (ii) in Theorem 2 can be rewritten in the form (iii) d dx h âˆ‘ âˆž n =0 c n ( x a ) n i = âˆ‘ âˆž n =0 d dx [ c n ( x a ) n ] (iv) R h âˆ‘ âˆž n =0 c n ( x a ) n i dx = âˆ‘ âˆž n =0 R c n ( x a ) n dx 2. Although Theorem 2 says that the radius of convergence remains the same when a power series is dfferentiated or integrated, this does...
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 Spring '08
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 Calculus, Power Series, power series representation

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