Given: parallelogram ABCD, AE ⊥ BC, AF ⊥ CD. To prove: ΔABE ∽ ΔADF. 1. m∠AEB = 90° Given AE ⊥ BC. 2. m∠AFD = 90° Given AF ⊥ CD. 3. ∠AEB ≅ ∠AFD Both have equal measures. 1,2 4. ∠B ≅ ∠D Opposite interior ∠s of parallelogram ABCD are ≅. 5. ΔABE ∽ ΔADF If 2 ∠s of one Δ are ≅ 2 ∠s of another Δ the Δs are ∽. 3,4 Edwin