The series $-2+10-50+250$ can be written using sigma notation (also called summation notation):
> $\large\displaystyle\sum\limits_{k=0}^{m}{{a_k}}$
**Find $m$.**
$m=$ [[☃ numeric-input 2]]
**Write an expression for $a_k$ in terms of $k$.**
$a_k=$ [[☃ expression 1]]