Janet is designing a frame for a client. she wants to prove to her client that m∠1 = m∠3 in her sketch. what is the missing justification in the proof? segment cd intersects segment ab, creating angles 1, 2, 3, and 4. statement justification segment cd intersects segment ab given ∠1 + ∠ 2 = 180° ∠ 2 + ∠3 = 180° ∠1 + ∠ 2 = ∠ 2 + ∠3 transitive property ∠1 = ∠3 subtraction property definition of supplementary angles intersecting lines postulate same-side interior angles theorem vertical angles theorem