Draw a line segment ABAB and bisect it. Also, bisect one of the equal parts.
Answer:
Draw a line segment AB.AB. With center AA and radius more than half of ABAB, draw arcs one on each side of ABAB. With center BB and same radius, draw arcs cutting previous arcs at PP and QQ respectively. Join PQPQ and which intersect ABAB at CC. With center AA and radius more than half of ACAC, draw arcs on each side of ACAC. With center CC and same radius, draw arcs cutting previous arcs at RR and SS respectively. Join RSRS and which intersect ACAC at DD.