Question

How do you find the sum of the arithmetic series `Sigma(42-9k)` from k=7 to 11?

Answer 1

`-195`

Explanation:

`sum(42-9k)` from `k=7` to `11` is a math problem. It is basically saying, starting when `k` equals `7` solve the expression of `42-9k`. Then, add that value to when `k=8`, `k=9`, `k=10` and `k=11`. Here's what that looks like:
`(42-9*7)+(42-9*8)+(42-9*9)+(42-9*10)+(42-9*11)`. This can be simplified to `-21+ -30+ -39+ -48+ -57`, which is `-195`.