Steps of construction:Construct a ray OBUsing the protractor construct ∠AOB of 80oConsidering O as centre and convenient radius construct an arc cutting the sides OA and OB at the points Q and PConsidering Q as centre and radius more than half of the angle PQ, construct an arcConsidering P as the centre and radius more than half of the angle PQ, construct another arc which intersects the previous arc at the point RJoin the points OR and produce it in order to from a ray OXTherefore, OX is the bisects of the ∠AOBSo the measure of each parts of the bisected angle is ∠AOX=∠BOX=40o