Solution: point d is the symmetrical point of point b about AC

∴PD=PB

Connect DQ AC to point p.

At this time ∴, the circumference △△pbq is the smallest.

CD=2 CQ= 1

DQ= root number 5

Because DQ=PQ+PB BQ= 1.

So the circumference of △PBQ is (1+ root number 5) cm.