解答:(1)证明:∵E是AD的中点,∴AE=DE,∵AF∥BC,∴∠AFB=∠DBE,在△AEF和△DEB中 ∠AEF=∠DEB ∠AFE=∠DBE AE=DE ∴△AEF≌△DEB(AAS),∴AF=BD;(2)四边形AFCD是菱形,证明:∵D为BC的中点,∴CD=BD,∵AF=BD,∴AF=CD,∵AF∥BC,∴四边形AFCD是平行四边形,∵AC⊥AB,∴∠CAB=90°,∵D为BC的中点,∴AD=DC,∴四边形AFCD是菱形.