∫≈A = 45，AC‖BD

It can be proved that △ACO and △BDO are isosceles right triangles.

∴AO=√2km,BO=2√2km

∴AB=√2+2√2=3√2km

②

Foundation: The point with equal distance at both ends of the line segment is on the middle vertical line of this line segment.

∴ Connect AB and handle it. The bisector and l intersect at point p, which is the demand.

Perpendicular bisector law;

Draw an arc with point A and point B as the center and half the length of AB as the radius (note that the two radii should be equal and the compass should not move). Two arcs will have an intersection on both sides of AB, connecting the two intersections and intersecting L at point P, which is the demand.