For people who are learning how to do basic geometry, this video will show you how to draw a perpendicular line from a point on a line using only a compass and pencil. You should first take your compass and place it on the center of the point on the line, drawing an even semicircle around the point. Then, finding the points where the semicircle intersects your original line, place the center of your compass on this point and then draw some arcs over where your point is. Repeat this on both sides. The point where your two arcs intersect is a point in the center which is perpendicular to your original point. Simply draw a line from your original point to this new point in order to draw a perpendicular line.