arithmetic
posted by Daniel on .
How do you find the sum number of an arithmetic sequence? I forgot and my textbook does not explain it well.

depends what information you know
1. If you know the first term a, and the common difference d, and the number of terms n, then
Sum(n) = n/2[2a + (n1)d]
2. If you know the first term a and the last term l, and the number of terms n, then
Sum(n) = n/2(a+l) 
N = the term number right?

I'm not sure what you mean by "term number."
"n" typically refers to how many units you have, how many numbers you are dealing with, the number of scores.
"a" is the value of the first number. Is that what you mean by "term number"?
I hope this helps a little more. Thanks for asking.