Answer:
Linear Pair Theorem
m∠2
∠3
definition of congruent angles
Step-by-step explanation:
1. ∠1 and ∠2 form a linear pair of angles, so ∠1 and ∠2 are supplementary by the Linear Pair Theorem.
2. Therefore, m∠1 + m∠2 = 180°, by the definition of supplementary angles.
3. It is given that ∠2 ≅ ∠3, so m∠2 = m∠3 by the definition of congruent angles.
4. By substitution, m ∠1 + m∠3 = 180°, so ∠1 and ∠3 are supplementary by the definition of supplementary angles.
