We are given the following picture
We are given the following statements
- Line BA is congruent to line OC
- Line ON is congruent to line DA
- Angle A is congruent to angle O
If we highlight the congruencies we get
where the matching colors indicate congruency. As we can see, we have a pair of sides that are congruent and the included angle are also congruent. This is the condition for the SAS theorem to apply. Hence both triangles are congruent by the SAS theorem