If the straight line passes through point A (3,0), then b =;;
If the straight line passes through point B (3, 1), then b =;;
If the straight line passes through point C (0, 1), then b =1;
① If the intersection of the straight line and the polyline OAB is on OA, that is, 1≤b≤, as shown in Figure ①.
At this time E(2b, 0)
∴S=OE? CO=×2b× 1=b
② If the intersection of straight line and polyline OAB is on BA, then < b
At this time, E(3,), d (2b-2, 1).
∴S=S moment -(S△OCD+S△OAE+S△DBE)
=3-[(2b-2)× 1+×(5-2b)? ()+×3()]=
∴S=.