Let's fill in the blanks with appropriate answers to complete the proof for triangle ABC being isosceles.
- Blank space 4: \( \overline{BD} \)
- Blank space 6: \( \overline{BD} \)
- Blank space 7: the Side-Angle-Side (SAS) Postulate
- Blank space 8: \( \overline{AB} \)
- Blank space 9: \( \overline{CB} \)
The completed proof is as follows:
In triangle ABC, it is given that angle A is congruent to angle C and angle ABD is congruent to angle CBD.
By the reflexive property, \( \overline{BD} \) is congruent to \( \overline{BD} \). Then, triangle ABD is congruent to triangle CBD by the Side-Angle-Side (SAS) Postulate.
Therefore, \( \overline{AB} \) is congruent to \( \overline{CB} \) because corresponding parts of congruent triangles are congruent.
By definition, triangle ABC is isosceles.