## Basic College Mathematics (10th Edition)

$\angle$SON = $\angle$TOM $\angle$TOS = $\angle$MON
Two angles that share the same number of degrees are congruent. Vertical Angles are the pairs of opposite angles made by two intersecting lines. Therefore $\angle$SON = $\angle$TOM and $\angle$TOS = $\angle$MON since they are vertical angles.