How could this be simplified in summation notation:
5 * y1 + 25 * y2 + 125 * y3
Thanks!
$\displaystyle 4 \times \xi + 4 \times \xi^2 + 4 \times \xi^3 + 4 \times \xi^4$
$\displaystyle = 4( \xi + \xi^2 + \xi^3 + \xi^4)$
$\displaystyle = 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
$\displaystyle ~ =~ 4 \sum_{r=1}^{4}{x_i}^r$