It is proved that BE is extended to point E, so that BE = CN, connecting line DE ∶ DB = DC ∠ BDC =120 ∴∠ ABC = ∠ ACB = 60 ∠△ ABC is an equilateral triangle ∴∠ ABC = ∠. N = 60 ∴∠ BDM+∠ BDE = 60, that is ∠ EDM = ∠ NDM = 60 ∵ DE = DNDM is male * * ∴ △ DMN △ DME \