<u><em>Answer:</em></u>
DE is the common side in the two triangles
<u><em>Explanation:</em></u>
The side of the triangle is named based on its start and end points
A triangle is named based on its three vertices where each two vertices would join forming a side
<u>For ΔDEC, the sides are:</u>
DE, EC and DC
<u>For ΔEDB, the sides are:</u>
ED, DB and EB
By comparing the two triangles, we would find that DE is the common side in both triangles
Note: The visual illustration is in the attached image
Hope this helps :)