∵MB∥CD、AD∥BC
∴△MBF∽△CFD,△EFD∽△CFB,
∴MF/BF=CF/DF,FE/FD=FC/FB,
∴MF=(CF*BF)/DF(1),FE=(FD*FC)/FB(2)
∴(1)*(2)得:FC^2=MF*FE