Question

What is the missing step of Given: AE ∥ FD, EC ≅ BF and ∠ABF≅∠ECD. Prove: AB ≅ CD. 1. AE ∥ FD. EC ≅ BF. ∠ABF≅∠ECD. Given.
2. ∠ABF and ∠FBD are supplementary. If two angles form a linear pair, then they are supplementary.
3. ∠ECD and ∠ECB are supplementary. If two angles form a linear pair, then they are supplementary.
4. ∠FBD≅∠ECB. If two angles are supplements of the same angle (or congruent angles), then they are congruent.
5 _
6. △AEC≅△DFB. AAS.
7. AC ≅ BD. Corresponding Parts of Congruent Triangles are Congruent (CPCTC)
8. BC ≅ BC. Reflexive Property
9. AB ≅ CD. Congruent segments subtracted from congruent segments form congruent segments

Answer 1

5. ∠AEC ≅ ∠DFB. From AE ∥ FD, EC and FB are transversals so the corresponding/alternate interior angles ∠AEC and ∠DFB are congruent.