∠ACB =∠ACD+∠DCB = 60； Similarly, ∠ ECD = ∠ ECA+∠ ACD = 60, ∴∠DCB=∠ECA.

In △DCB and △ACE, AC=BC, DC=EC, ∠DCB=∠ECA,

∴△DCB≌△ACE, (edge, angle, edge), ∴∠ b = ∠ CAE = 60.

∠∠CAE =∠∠ACB = 60°, ∴AE∥BC (the offset angles are equal and the two lines are parallel).