Solution: Because EF is perpendicular to AB, CD is perpendicular to AB (known).

Therefore, EFD angle = 90, CDB angle = 90 (vertical definition).

Because angel ·EFD = angel ·CDB

So EF//CD (same angle, two straight lines are parallel)

So the angle 1= angle CDE (two straight lines are parallel and the internal dislocation angles are equal).

Because the angle 1= angle 2 (known)

So angle CDE= angle 2

So ED//CB (internal dislocation angles are equal and two straight lines are parallel)