Question

-7+12-17+22-27
What is a possible expression for the series

Answer 1

just x-17 because you just reduce this in the calculator

Answer 2

Signs start with a negative and alternate, so the general term will have (-1)^n as a factor. The common difference has a magnitude of 5, so the general term is

$a_{n}=(-1)^{n}\cdot (7+5(n-1))$

and the sum is

$\displaystyle S=\sum_{n=1}^{5}{(-1)^{n}\cdot (5n+2)}=-17$