(1)证明:∵AD∥BC,∴∠C+∠ADE=180°.
∵∠BFE=∠C,∴∠AFB=∠EDA.
∵AB∥DC,∴∠BAE=∠AED.
∴△ABF∽△EAD.
(2)∵AB∥CD,BE⊥CD,∴∠ABE=90°,
∵AB=4,∠BAE=30°,∴AE=
=
=
.
(3)∵△ABF∽△EAD,∴
.∴BF=
.
(1)证明:∵AD∥BC,∴∠C+∠ADE=180°.
∵∠BFE=∠C,∴∠AFB=∠EDA.
∵AB∥DC,∴∠BAE=∠AED.
∴△ABF∽△EAD.
(2)∵AB∥CD,BE⊥CD,∴∠ABE=90°,
∵AB=4,∠BAE=30°,∴AE=
=
=
.
(3)∵△ABF∽△EAD,∴
.∴BF=
.