In δabc shown below, line segment ab is congruent to line segment bc: triangle abc, where sides ab and cb are congruent given: line segment ab≅line segment bc prove: the base angles of an isosceles triangle are congruent. the two-column proof with missing statement proves the base angles of an isosceles triangle are congruent: statement reason 1. segment bd is an angle bisector of ∠abc. 1. by construction 2. ∠abd ≅ ∠cbd 2. definition of an angle bisector 3. segment bd ≅ segment bd 3. reflexive property 4. 4. side-angle-side (sas) postulate 5. ∠bac ≅ ∠bca 5. cpctc which statement can be used to fill in the numbered blank space?