Given the points a(0, 0), b(e, f), c(0, e) and d(f, 0), determine if line segments ab and cd are parallel, perpendicular or neither.

a. parallel
b. perpendicular
c. neither

The slope:
m = rise / run;
For the line segment AB:
m AB = (y 2 - y 1) /(x 2 - x 1) = ( f - 0 ) / ( e - 0 ) = f / e
For the line segment CD:
m CD = ( 0 - e ) / ( f - 0 ) = - e / f
m CD = - 1 / m AB

The lines are  B ) perpendicular