Chapter 9 - Sequences and Series - 9-2 Arithmetic Sequences - Practice and Problem-Solving Exercises - Page 577: 69

$a_1=52$ $d=-10$

With $a_3=32$, the value of $a_7$ can be found by adding the common difference $d$ four times. Since $a_3=32$, then \begin{align*} a_7&=a_3+4d\\\\ -8&=32+4d\\\\ -8-32&=4d\\\\ -40&=4d\\\\ \frac{-40}{4}&=\frac{4d}{4}\\\\ -10&=d \end{align*} The value of $a_1$ can be found by subtracting $d$ from $a_3$ two times. Thus, \begin{align*} a_1&=a_3-2d\\ a_1&=32-2(-10)\\ a_1&=32+20\\ a_1&=52 \end{align*}