Verify Triangle Side BD in Triangle ABD: True or False

To solve this problem, we begin by recalling that a triangle is defined by three vertices, and the sides of the triangle are the line segments connecting these vertices. In $\triangle ABD$, the vertices are $A$, $B$, and $D$. The sides of the triangle are therefore the segments that connect these points in pairs.

Let us now consider each segment that forms the sides of $\triangle ABD$:

• AB connects vertices $A$ and $B$.
• BD connects vertices $B$ and $D$.
• AD connects vertices $A$ and $D$.

Since line segment $BD$ connects two of the vertices of the triangle ($B$ and $D$), it is one of the sides of $\triangle ABD$ by definition.

Therefore, the statement "BD is a side of the triangle ABD" is True.