1. ABCD is a parallelogram
2. AC bisects ∠BCD and ∠BAD
3. BD bisects ∠CDA and ∠ABC
4. ∠ABE ≅ ∠CBE;
∠ADE ≅ ∠CDE
5. ∠ABE and ∠CDE are alt. int. ∠s
5. def. of alternate interior angles
6. ∠ADE and ∠CBE are alt. int. ∠s
6. def. of alternate interior angles
7. ∠ABE ≅ ∠CDE;
∠ADE ≅ ∠CBE;
7. alternate interior angles are congruent
8. ∠ABE ≅ ∠ADE ≅ ∠CDE ≅ ∠CBE
9. ∠BAE ≅ ∠BCE ≅ ∠DCE ≅ ∠DAE
9. similar argument as steps 4 - 8
10. diagonals of a parallelogram bisect each other
11.△ABE ≅ △CBE ≅ △CDE ≅ △ADE