Answer:
Apply the SAS postulate (see details below).
Step-by-step explanation:
(1) because triangles ABC and BCD share one side BC, both are right-angled, and we are given that |AC|=|BD|, by the Pythagorean theorem, we know that also the third sides are congruent: |AB|=|CD|.
(2) By application of the SAS postulate, where the two sides |AB|=|CD|, |CB|=|CB|, and the included angle <ABC=<CBD, it follows that the triangles ABC and BCD are congruent.
(I am using |..| notation for length of a segment)
