What else must you know to prove the triangles are congruent by sas?

AD must be congruent to BC in order to prove the two triangles are congruent by SAS.

Step-by-step explanation:

As we have to prove the triangle congruency by SAS or Side-Angle-Side congruency, so two consecutive side along with their common angle must be congruent with the other triangle.

As in ΔABC and ΔADC already

So, if AD becomes congruent to BC, then both the triangle will be congruent.

This will happen when ABCD becomes a parallelogram or rhombus or rectangle or square. Because in all of these geometric figure opposite sides are congruent.