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

1 Answer
Dec 24, 2016

-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.