To construct an angle bisector for an angle$\angle \mathrm{AOB}$, the first arc is drawn with ____ as the Centre.

• Take any width of radius in a compass and with O as the Centre, draw two arcs such that it cut the rays OA and OB at points C and D respectively.
• Without changing the distance between the legs of the compass, draw two arcs with C and D as centres, such that these two arcs intersect at a point named E.
• Join the ray OE. This is the required angle bisector of angle AOB.

Therefore, to construct an angle bisector for an angle$\angle \mathrm{AOB}$, the first arc is drawn with O as the Centre.