Answer:
The reason for the third step in this proof : Opposite angles of parallelogram are equal
Step-by-step explanation :
Given: Quadrilateral PQRS is a rectangle.
To prove: PR = QS
Proof: 1. Given that Quadrilateral PQRS is a rectangle.
2. Definition of a rectangle : Rectangle PQRS is a parallelogram
3. QP ≅ RS QR ≅ PS (Opposite angles of parallelogram are equal).
4. m∠QPS = m∠RSP = 90° (definition of a rectangle)
5. Δ PQS ≅ ΔSRP (SAS criterion for congruence)
6. PR ≅ QS (Corresponding sides of congruent triangles are congruent).
7. PR = QS (Congruent line segments have equal measures).
Therefore, The reason for the third step in this proof : Opposite angles of parallelogram are equal