Final answer:
The question appears to fall under High School level Geometry, where properties of congruent triangles might be applied to find the length of side DC in triangle EDC, given that ABC = EDC and the lengths of AB and BC.
Step-by-step explanation:
The student's question seems to relate to the topic of geometry and triangles specifically, given that they are asking for the length of a side of a triangle (DC) when they have information about the other sides (AB and BC) and the fact that two triangles, ABC and EDC, are congruent. This implies that we could apply the properties of congruent triangles to find the length of the unknown side. However, the given information is insufficient to directly calculate the length of DC unless additional information is provided, such as the angles of the triangles or that they are special types of triangles (e.g., right triangles).