Redraw Figure 1 shown below:
The side AD is equal to AB.
The side CD is equal to CB.
There is one common side AC.
Therefore, it can be observed that there are three sides are equal.
Therefore, it can be SSS congruence criterion that can be use to prove ABC and ADC are congruent.
Thus, the SSS congruence criterion is used to prove triangles ABC and ADC are congruent.