Study mathematics by doing it
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Problems discussionThu, 21 Jun 2018 12:17:58 +0000enhourly1http://wordpress.com/https://s0.wp.com/i/buttonw-com.pngStudy mathematics by doing it
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Independent University of Moscow. Algebra-1. Ex. sheet №2
https://liberium.wordpress.com/2011/09/16/independent-university-of-moscow-algebra-1-exc-sheet-%e2%84%962/
https://liberium.wordpress.com/2011/09/16/independent-university-of-moscow-algebra-1-exc-sheet-%e2%84%962/#respondFri, 16 Sep 2011 08:06:22 +0000http://liberium.wordpress.com/?p=182Problem 1. Find formula for sum of two formal series.

Solution.

Problem 2. Find formula for product of two formal series.

Solution.

Theorem 1. Series is invertible iff

Proof. Indeed, if , then series with evidently has no inverse. Conversely if , then an inverse of the series is with