Respuesta :
Answer: opposite sides in rectangle are congruent.
Step-by-step explanation:
It is given that Quadrilateral PQRS is a rectangle.
Since opposite sides of rectangle are congruent.
Therefore ,  QP ≅ RS, QR ≅ PS
Therefore, the reason for "QP ≅ RS, QR ≅ PS" in this proof is "opposite sides in rectangle are congruent."
hence, the reason for the third step in this proof is  "opposite sides in rectangle are congruent."
Answer:
Since, the opposite sides of parallelogram are always congruent.
With using this property, the proof is mentioned below,
Given : Quadrilateral PQRS is a rectangle.
To Prove: PR = QS
   Â
Quadrilateral PQRS is a rectangle   ( Given )
Rectangle PQRS is a parallelogram. Â ( Definition of a rectangle )
QP ≅ RS QR ≅ PS        ( By the definition of parallelogram)          Â
m∠QPS = m∠RSP = 90°    ( Definition of a rectangle )
Δ PQS ≅ ΔSRP            (SAS criterion for congruence )
PR ≅ QS    ( Corresponding sides of congruent triangles are congruent)
PR = QS Â Â Â ( Congruent line segments have equal measures )
Hence proved.