∫M. n. g. h is the midpoint of AE, AB, BD and DE respectively.
∴ ng ∨ =1/2amdh ∨ =1/2admn ∨ =1/2beg =1/2be (quadrilateral is a parallelogram).
CA = CB，CD=CE，∠ACB =∠DCE = 90°
∴ ad = be △ ACD △ BCE (quadrangle is diamond)
∴ angle EBC= angle CAD GH∨= 1/2be∴ angle EBC= angle HGD.
∫MH∨= 1/2ad ∴∠cad =∠HMC∴ Angle HGD=∠HMC.
∴∠ACG=∠GNM =90
∴ Quadrilateral MNGH is a square.