According to Theorem 6.4, the opposite angles in parallelogram GFBA are congruent.
∠F≅ ∠A
Opposite angles in parallelogram HACD are also congruent.
∠A≅ ∠D
These observations let us write a chain of congruent angles.
∠F≅ ∠A≅ ∠D
Using the transitive property of congruence, we can conclude that angles ∠F and ∠D are congruent. We can summarize the process above in a two-column proof.
Completed Proof
2
&Given:&& GFBAis a parallelogram
& && HACDis a parallelogram
&Prove:&& ∠F≅∠D
Proof:
