# Multiplying summations?

1. on #1 c) of the homework:
http://www.math.ubc.ca/~oyilmaz/courses/m267/hmk3.pdf [Broken]
how do i multiply this summation?

## Homework Equations

3. what i did was i multiplied the 2 expos and made on of the k indexes a 'm' instead and i got $$\sum ei(k+m)t$$

Last edited by a moderator:

$$\left( \sum_{k =1}^{N_1} f(k) \right) \left( \sum_{j=1}^{N_2} g(j) \right) = \sum_{k=1}^{N_1} \sum_{j=1}^{N_2} f(k)g(j)$$