How do you find the sum of the first 14 terms of the arithmetic series 11+7+3+...?
There are several formula we need to keep in mind when working with arithmetic series
1) common difference
2) last term :
3) Arithmetic sum:
An alternative formula is
Now we can begin to work this problem
We have an arithmetic series begin at 11, 7, 3 ......
We know that
Let's find the following
Let's substitute it into the sum formula
If we use the alternative formula, we will still get the same answer