1) place the compass needle on the external point r.2) make the compass width greater than the distance from r to the given line. 3) draw an arc cutting the given line at two points. 4) mark and label the points of intersection p and q. 5) without changing the compass width, move the compass needle to q and draw another arc below the line crossing the previous arc. 6) move the compass needle to p and make an arc below the line. 7) mark and label the point of intersection s. 8) draw a line from the external point r to the point where the arcs intersect, s. 9) line rs is perpendicular to line pq and passes through the external point r.
