You know how when you ask your mom or dad WHY you have to do something, they inevitably reply, "Because I said so!" While that's a perfectly acceptable answer in the scope of parenting, it is not adequate when constructing proofs.

Geometry 4(A) distinguish between undefined terms, definitions, postulates, conjectures, and theorems

Geometry 6(A) verify theorems about angles formed by the intersection of lines and line segments, including vertical angles, and angles formed by parallel lines cut by a transversal and prove equidistance between the endpoints of a segment and points on its perpendicular bisector and apply these relationships to solve problems