### Using ruler and compass only, draw a right angle.

1.  Draw a ray $OA$. OA
2.  With $O$ as the center and any convenient radius, draw an arc, cutting $OA$ at $P$. OA P
3.  With $P$ as the center and the same radius, draw an arc, cutting the arc drawn in step 2 at $Q$. OA PQ
4.  With $Q$ as the center and the same radius, draw an arc, cutting the arc drawn in step 2 at $R$. OA PQR
5.  With $Q$ as the center and the same radius, draw an arc. OA P Q R
6.  With $R$ as the center and the same radius, draw an arc, cutting the arc drawn in the previous step at $B$. OA P Q R B
7.  Draw $OB$ and produce it to $C$.$\angle AOC$ is the angle of measure $90^\circ$. OA P Q R B C 90°