Show that the quadrilateral with vertices $A (-5, 4)\text{,}$ $B (7, -11)\text{,}$ $C (12, 25)\text{,}$ and $D(0, 40)$ is a parallelogram. (Hint: Show that $\overline{AB}$ is parallel to $\overline{CD} \text{,}$ and that $\overline{BC}$ is parallel to $\overline{AD} \text{.}$) The slope of $\overline{AB}$ is , and the slope of $\overline{CD}$ is . These slopes are ? equal different , so the sides are ? parallel perpendicular . The slope of $\overline{BC}$ is , and the slope of $\overline{AD}$ is . These slopes are ? equal different , so the sides are ? parallel perpendicular .