Showing posts with label Cauchy Product. Show all posts
Showing posts with label Cauchy Product. Show all posts

Saturday, April 16, 2011

Cauchy Product (1 − 1 + 1 − 1 + ... )

Perquisites :


 given


Cauchy product
\begin{array}{rcl}
c_n & = &\displaystyle \sum_{k=0}^n a_k b_{n-k}=\sum_{k=0}^n (-1)^k (-1)^{n-k} \\[1em]
 & = &\displaystyle \sum_{k=0}^n (-1)^n = (-1)^n(n+1).
\end{array}
then, the product is 
\sum_{n=0}^\infty(-1)^n(n+1) = 1-2+3-4+\cdots.
therefore,
(1)
based  on geometric series (GS.ID.1)
 \sum_{k=0}^{n} a r^k = \frac{a}{1-r}. 
(2)
a=1 , r=-1 in the following equation
(3)
from (2) and (3)
(4)


from (1) and (4)

Wednesday, April 6, 2011

Cauchy Product (Series convolution )

This post will help students understand the derivation of harmonic series through Cauchy Product 

Given identities:

Logarithmic Function

 
(1)
Geometric Series


(2)
Harmonic Series
(3)
product of (1) and (2)

 based on (SC.ID.1)
  

therefore,

therefore, 


(4)
if x=1/2
 

Integration of (4)