# Summation Notation Problem

• Feb 23rd 2009, 10:40 PM
genkislaw
Summation Notation Problem
How could this be simplified in summation notation:

5 * y1 + 25 * y2 + 125 * y3

Thanks!
• Feb 23rd 2009, 10:47 PM
Welcome to the forum (Party)

$5 \times y^1 + 25 \times y^2 + 125 \times y^3$

$(5\times y)^1 +(5\times y)^2 + (5\times y)^ 3$

$
\sum_{r= 1}^{3}{(5\times y)^r}

$
• Feb 23rd 2009, 10:50 PM
genkislaw

4 * x(sub)i + 4 * x(sub)i^2 + 4 * x(sub)i^3 + 4 * x(sub)i^4

Thanks!
• Feb 23rd 2009, 10:55 PM
Quote:

Originally Posted by genkislaw

4 * xi + 4 * xi^2 + 4 * xi^3 + 4 * xi^4

Thanks!

$4 \times \xi + 4 \times \xi^2 + 4 \times \xi^3 + 4 \times \xi^4$

$= 4( \xi + \xi^2 + \xi^3 + \xi^4)$

$= 4 \sum_{r=1}^{4}{\xi}^r.....\text{I can't really understand x(sub)i but you can put it in place of }\xi$

Guess : I think you mean x_i ...if its so then your answer is

$~ =~ 4 \sum_{r=1}^{4}{x_i}^r$
• Feb 23rd 2009, 11:17 PM
genkislaw
Thanks!