Using ruler and compasses only, draw a right angle.

Explanation

1. Construct a ray OA.

2. Taking O as center and convenient radius construct an arc PQ using a compass intersecting the ray OA at the point P.

3. Taking P as center and same radius construct another arc which intersects the arc PQ at the point R.

4. Taking R as center and same radius, construct an arc which cuts the arc PQ at the point C opposite to P.

5. Using C and R as the center construct two arcs of radius which is more than half of CR which intersects each other at the point S.

6. Now join the points O and S and extend it to the point B.

Here, `angleAOB` is the required angle of `90^*`.