# How do you find the sum of the first 14 terms of the arithmetic series 11+7+3+...?

##### 1 Answer

#### Explanation:

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

#color(red)(a_14= -41)#

Let's substitute it into the sum formula

#S= 7(-30)#

#S= -210#

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If we use the alternative formula, we will still get the same answer