We will use the SAS (SIDE-ANGLE-SIDE) to prove that the two triangles are congruent. This states that if two sides and the included angle in one triangle are congruent to two sides and the included angle of another triangle, then the two triangles are congruent.
First line
First column: AB is congruent to CB Second column: Given
Second line
First column: angle ABD is congruent to angle CBD Second column: Given
At this point we have the SIDE-ANGLE portion of SAS. We just need the other side. We can see from the given angles that they both share a side...BD.
Third Line
First column: BD is congruent to BD Second column: Reflexive property
All that is left is to state SAS.
Fourth Line
First Column: Triangle ABD is congruent to triangle CBD Second column: SAS (from lines 1,2,3)
