答案：(a) $S’=(5,12)$, $T’=(-3,7)$ (b) $\dfrac{5}{8}$
- $S'(5,12)$, $T’=(-3,7)$
- $S’T’$ 的斜率
$\begin{array}{cl}
= & \dfrac{7-12}{-3-5} \\
= & \dfrac{-5}{-8} \\
= & \dfrac{5}{8}
\end{array}$
