如图,AB‖CD,AD‖BC,AE⊥AB,AF⊥AD,AE=AB,AF=AD,试说明AC=EF

AB‖CD,AD‖BC
ABCD是平行四边形
AE⊥AB,AF⊥AD
∠EAF+∠BAD=360°-2*90°=180°
∠ABC+∠BAD=180°
∠EAF=∠ABC
AE=AB,AF=AD=BC
△EAF≌△ABC
AC=EF,得证.