DF=EF证明：延长BC 并作DB//EH 交BC延长线于H∵ DB//HE ∴ ∠ABC = ∠FHE,∵ AB=AC,∴ ∠ABC = ∠ACB∴ ∠FHE = ∠ACB ∵ ∠HCE 与 ∠ACB是对顶角,∴ ∠HCE = ∠CHE ∴ CE=HE由题意,DB=HE∵ DB=HE,角DBC = 角FHE,角D...