Answer:
Side-side-side postulate
Step-by-step explanation:
In the first statement, we are given that AC = BD ....... (1){It is given}
Now, in the second statement, we are given that AB = DC ...... (2){ Because the parallelogram has equal opposite sides}
Now, again we are given that AD = DA ........... (3) {From the symmetric property}
Now, conditions (1), (2), and (3) are applicable to say that Δ ABD and Δ ACD are congruent.
Since there are three sides involved to say Δ ABD ≅ Δ ACD, so it is by Side-side-side postulate. (Answer)