Triangle ABC: Calculate the Perpendicular Height from Vertex A

In the given diagram, we need to determine the height of triangle $\triangle ABC$. The height of a triangle is defined as the perpendicular segment from a vertex to the line containing the opposite side.

Upon examining the diagram:

• Point $A$ is at the top of the triangle.
• The side $BC$ is horizontal, lying at the base.
• Line segment $AD$ is drawn from point $A$ perpendicularly down to the base $BC$ at point $D$. This forms a right angle at $D$ with line $BC$.

Therefore, line segment $AD$ is the perpendicular or the height of triangle $\triangle ABC$.

Consequently, the height of triangle $\triangle ABC$ is represented by the segment $AD$.