Answer:
Σ = -591
Explanation:
index (where you start) = i=5
number you end with = 14
formula for nth term: (-7-6i)
First identify the numbers you will need to plug in:
5, 6, 7, 8, 9, 10, 11, 12, 13, 14
Plug those numbers in, similar to how you would plug in an x-value in a linear equation.
So for example, 10:
-7-6(10)= -7-60 = -67
Do this for each of the numbers you identified above.
You should get the following for each number (respectfully):
-37, -43, -55, -61, -67, -73, -79. -85, -91
Add these numbers together (Σ (sigma) means "sum" (at least in this context)):
Σ = -591
I might have made a few calculation errors, so I suggest that you double check everything just to make sure. This is how my Algebra II teacher taught me to do it, so there may be other ways.