请输入您要查询的字词:

 

单词 ExampleOfCauchyMultiplicationRule
释义

example of Cauchy multiplication rule


Let us form the Taylor expansionMathworldPlanetmath of  exsiny  starting from the known Taylor expansions

ex=1+x+x22!+x33!+,
siny=y-y33!+y55!-y77!+-

and multiplying these series with Cauchy multiplication rule. As power seriesMathworldPlanetmath, both series are absolutely convergent for all real (and complex) values of x and y. The rule gives immediately the series

y+(-y33!+xy)+(y55!-xy33!+x2y2!)+(-y77!+xy55!-x2y32!3!+x3y3!)+(y99!-xy77!+x2y52!5!-x3y33!3!+x4y4!)+(1)

The parenthesis expressions here seem a bit irregular, but we can regroup and rearrange the terms in new parentheses:

exsiny=y+xy1!1!+(x2y2!1!-y33!)+(x3y3!1!-xy31!3!)+(x4y4!1!-x2y32!3!+y55!)+(2)

It’s clear that the last series precisely the same terms as the preceding one. The regrouping and the rearranging of the terms is allowable, since also (1) is converges absolutely. In fact, if one would multiply the series of ex with the series y+y33!+y55!+ of sinhy (which converges absolutely x), one would get the series like (1) but all signs “+”; by the Cauchy multiplication rule this series converges especially for each positive x and y, in which case it is a series with positive terms; hence (1) is absolutely convergent.

The form (2) can be obtained directly from the Taylor series formula (http://planetmath.org/TaylorSeries).

随便看

 

数学辞典收录了18232条数学词条,基本涵盖了常用数学知识及数学英语单词词组的翻译及用法,是数学学习的有利工具。

 

Copyright © 2000-2023 Newdu.com.com All Rights Reserved
更新时间:2025/5/4 12:49:52