Farmer Mansfield wants to find whether the straight pipes are parallel. The distance from barn B to the north end of pipe 1 is 143 ft, and from there to the north end of pipe 2 is 42 ft. The distance from the barn to the south end of pipe 1 is 121 ft, and from there to the south end of pipe 2 is 33 ft. Are the pipes parallel? How do you know?
If the ends of the pipes are measured from the same barn (B), then there are not enough measurements to tell if the pipes are parallel or not. Some angle measurements are required.
With distance measurements from a single point, the pipes could "spin" around the barn, and the measurements would not change.