Be || cd 1. given 2. ∠a ≅ ∠a 2. reflexive property 3. ∠acd ≅ ∠abe 3. corresponding angles formed by parallel lines and a transversal are ≅. 4. ∠adc ≅ ∠aeb 4. corresponding angles formed by parallel lines and a transversal are ≅. 5. δabe ∼ δacd 5. aa similarity postulate 6. ac ab = ad ae 6. definition of similar triangles 7. ac = ab + bc, ad = ae + ed 7. 8. ab + bc ab = ae + ed ae 8. substitution 9. ab ab + bc ab = ae ae + ed ae 9. addition 10. bc ab = ed ae 10. subtraction fill in the missing reason for the proof. a) transitive property b) subtraction property c) sss similarity theorem d) segment addition postulate