perpendicular constructions

[Mattk]

my son has homework on the above.he has to do it armed only with a compass and a ruler.

any ideas ?!

[Clanad]

This site will describe what you need in far fewer words than I could... Best of luck!

http://www.answers.com/topic/ruler-and-compass-construction

[Octavius]

And here:

http://regentsprep.org/Regents/math/construc/perp.htm

[landie]

you can construct a perpendicular line by first

drawing a staight line.

mark the line with a compass about the point you want your perpendicular (you should now have a centre point and a mark each side.

open the compass further and, from each of the two marked points construct a circle,

You will note that the two circles intersect either side of the line.

A line drawn through the two intersections should also pass through the centre point on the line. This will be perpendicular to your original line.