### Draw a line segment $\overline{ PQ }.$ Take a point $R$ outside the line segment $\overline{ PQ }.$ Through $R,$ draw a line perpendicular to $\overline{ PQ }.$

1. Draw a line segment $\overline{ PQ }$ and mark a point $R$ such that it does not lie on the line segment $\overline{ PQ }.$
2. With $R$ as centre and an appropriate radius, draw an arc that intersects the line segment $\overline{ PQ }$ on two $2$ points $A$ and $B.$
3. With the same radius as in step $2,$ draw $2$ arcs with centres $A$ and $B$ respectively and mark the intersection of the arcs as point $S.$
4. Join $RS,$ the line segment $\overline{ RS }$ is the required perpendicular line to $\overline{ PQ }.$