# Extending the definition of the summation convention

1. Oct 4, 2013

### ppy

1. The problem statement, all variables and given/known data

let a$_{i}$=x$^{i}$ and b$_{i}$=1$\div$ i ! and c$_{i}$=(-1)$^{i}$ and suppose that i takes all interger values from 0 to ∞. calculate a$_{i}$b$_{i}$ and calculate a$_{i}$c$_{i}$

2. Relevant equations
i know that in suffix notation a$_{i}$b$_{i}$ is the same as the dot product as when you have to of the same subscripts you take the sum of a$_{i}$b$_{i}$ from i=1 to i=3 but i am not really sure
of how to use the part where it says take interger values of i from 0 to ∞ an explanation would be great .
thanks.

2. Oct 4, 2013

### tiny-tim

hi ppy!
it's asking you for ∑ xi/i! and ∑ (-1)ixi

3. Oct 4, 2013

### brmath

you actually run i from 1 to $\infty$ not 1 to 3