## Geometry: Common Core (15th Edition)

$\overline{OD}$
An altitude is a perpendicular line segment drawn from the vertex of a triangle to a side opposite the vertex. An altitude for $\triangle AOC$ is $\overline{OD}$ because it is a perpendicular line segment that originates at vertex $O$ and contacts $\overline{AC}$, which is the side opposite vertex $O$.