Answer:
Draw a line AB
Take a point C on AB
Fix the tip of compass at C and with a fix radius, cut AB on both sides of C
Mark those points D and E
Fix the tip of compass on D, and with the same radius, draw an arc above C
Do the same with E
Those two arcs will intersect at a point, mark the point F
Make a line passing through both C and F
Line CF is perpendicular to AB
