CPM Homework Help : CCG Problem 5-115

How many terms are in the arithmetic sequence shown below?

$15$ , $7$ , $-1$ , $-9$ , $\dots$ , $-225$

Hint:

Remember that the equation for an arithmetic sequence is:

$a_n=m(n-1)+a_1$

Step 1:

Find the common difference. Substitute the common difference into m and substitute the first and last term into the equation.

Step 2:

$n$ is the number of terms.
Solve the equation for $n$ .

Answer:

$n=31$ terms