A (0,2) B (5,4)
C(1,8) D( 3,3)
Apply the slope formula:
[tex]m=\frac{y2-y1}{x2-x1}[/tex]For AB
[tex]m=\frac{4-2}{5-0}=\frac{2}{5}[/tex]For CD
[tex]m=\frac{3-8}{3-1}=-\frac{5}{2}[/tex]So both slopes are negative reciprocals of each other.
They are perpendicular lines.