### Home > CCAA8 > Chapter 10 Unit 11 > Lesson CCA: 10.2.3 > Problem10-56

10-56.

How many terms are in the arithmetic sequence shown below?

$15,\ 7,\ −1,\ −9,...,\ −225$

Write an equation for the arithmetic sequence using $a_n−m\left(n-1\right)+a_1$

Let $a$ sub $n=−225$ and solve for $n$.