# Thread: Summation Notation Problem

1. ## Summation Notation Problem

How could this be simplified in summation notation:

5 * y1 + 25 * y2 + 125 * y3

Thanks!

2. Welcome to the forum

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

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

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

$

What about this, if I was putting it in summation notation using sigma?

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

Thanks!

4. Originally Posted by genkislaw

What about this, if I was putting it in summation notation using sigma?

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

$~ =~ 4 \sum_{r=1}^{4}{x_i}^r$

5. Thanks!