## Elementary Geometry for College Students (5th Edition)

$R$ is the point of intersection between lines $\overleftrightarrow{AB}$. The measures of $\angle1$ and $\angle2$ are equivalent.
Point R is the only point where both lines cross, so Point R is the point of intersection. The measures of vertical angles (angles opposite each other and formed by intersecting lines) are congruent. Angles 1 and 2 both fit this description, so the measures of $\angle1$ and $\angle2$ are equivalent.