## Geometry: Common Core (15th Edition)

a) Vertical Angles Theorem b) $\angle1\cong\angle6$ c) Vertical Angles Theorem d) Transitive Property of Congruence
$\angle3$ and $\angle6$ are vertical angles. Since $\angle1$ and $\angle6$ are both congruent to $\angle3$, they are congruent to each other. $\angle1$ and $\angle4$ are vertical angles. Since $\angle4$ and $\angle6$ are both congruent to $\angle1$, they are congruent to each other.