Consider the diagram and proof by contradiction. given: △abc with ∠b ≅ ∠c prove: ab ≅ ac it is given that ∠b ≅ ∠c. assume ab and ac are not congruent. if ab > ac, then m∠c > m∠b by if ac > ab, then m∠b > m∠c for the same reason. however, using the given statement and the definition of congruency, we know that m∠b = m∠c. therefore, ab = ac and ab ≅ ac. what is the missing reason in the proof? converse of the triangle parts relationship theorem substitution definition of congruency converse of the isosceles triangle theorem