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