Transitive Property Definition of COMPLEMENTARY Angles Subtraction Property
M∠1 + M∠2 = 90° and M∠2 + M∠3 =90°
M∠1 + M∠2 = M∠2 + M∠3 M∠1 = M∠3
Definition of Congruent Angles
∠1 ⩭ ∠3