2. Says ∠1 is supplementary to ∠2.
3. Says m∠1 + m∠2 = 180°.
Since the definition of supplementary angles tells you that supplementary angles sum to 180°, the appropriate choice for the reason is ...
... Definition of Supplementary Angles
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4. Says ∠1 ≅ ∠3
5. Says m1∠ = m3.
Since the Angle Congruence Postulate tells you that congruent angles have the same measure, the appropriate choice for the reason is ...
... Angle Congruence Postulate
