Exercise 5 Page 691

Explicit equations for the $n\text{th}$ term of an arithmetic sequence follow a certain format. In this form, $a_1$ is the first term in the sequence, $d$ is the common difference, and $n$ is the position of the desired term in the sequence. We are given that $a_1=10$ and $d=\text{-}5,$ so we can substitute these values to write the equation. Let's also simplify this equation. To find the value of the $9\text{th}$ term, we substitute $n=9$ into this equation and solve for $a_9.$ The $9\text{th}$ term in the sequence is $\text{-}30.$