## Geometry: Common Core (15th Edition)

$\angle AOB$ and $\angle COD$
$\angle AOD$ and $\angle AOB$ form a linear pair on $\overset\longleftrightarrow{DB}$. $\angle AOD$ and $\angle COD$ form a linear pair on $\overset\longleftrightarrow{AC}$. Linear pairs are supplementary.