Here’s how to organize the statements and reasons into a two-column proof that parallelogram ABCD is a rectangle:
Statements | Reasons --- | ---
- ABCD is a parallelogram. | Given
- DB≅AC | Given
- DA≅CB | Opposite sides of a parallelogram are congruent.
- AB≅BA | Reflexive Property of Congruence
- △BAD≅△ABC | SSS Congruence Theorem
- ∠BAD≅∠ABC | Corresponding Parts of Congruent Triangles are Congruent (CPCTC)
- m∠BAD = m∠ABC | Definition of congruence
- m∠BAD + m∠ABC = 180° | Consecutive angles of a parallelogram are supplementary
- m∠BAD + m∠BAD = 180° | Substitution (replacing m∠ABC with m∠BAD)
- 2m∠BAD = 180° | Combine like terms
- m∠BAD = 90° | Division Property of Equality
- m∠ABC = 90° | Transitive Property of Equality
- m∠ADC = m∠DAB = 90° | Opposite angles of a parallelogram are congruent
- ∠BAD, ∠DCB, ∠ABC, and ∠ADC are right angles | Definition of a right angle
- ABCD is a rectangle. | Definition of a rectangle
This arrangement uses the given information to show that ABCD has all the properties of a rectangle, particularly that all angles are right angles due to the congruence of the diagonals.