Extending the definition of the summation convention

[ppy]

Homework Statement

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$_{i}$

Homework 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.

 

[tiny-tim]

hi ppy!

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$_{i}$

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

 

[brmath]

from i=1 to i=3

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