If two lines are parallel they have the same slope, but if they are perpendicular the slope is the negative reciprocal of the original line.
To calculate the slope:
[tex]\begin{gathered} m=\frac{y_2-y_1}{x_2-x_1} \\ m_{AB}=\frac{-15-13}{4-(-3)} \\ m_{AB}=\frac{-28}{7}=-4 \end{gathered}[/tex][tex]\begin{gathered} m_{CD}=\frac{-7-5}{1-(-2)}_{} \\ m_{CD}=\frac{-12}{3}=-4 \end{gathered}[/tex]Their slope are the same, so the lines would be parallels.
