# How do you find the formula for #a_n# for the arithmetic sequence #a_1=-4, a_5=16#?

##### 1 Answer

May 8, 2017

Set up and solve a system of equations using the definition of the arithmetic sequence. Answer:

#### Explanation:

We know that from the general formula for arithmetic sequences:

where

So, we write out what we know:

Using the general formula for arithmetic sequences, the second equation becomes:

By substituting

Now, we simply solve for d:

Therefore, the formula for the given arithmetic sequence is: