A line and a point not on the line are contained in exactly one plane. If a line intersects a plane, but is not contained in the plane, then the intersection is exactly one point. Theorem 4 Two intersecting lines are contained in exactly one plane. On every line, there is a segment with a given point as an endpoint congruent to any given segment. For every ray, there is an angle with the given ray as a side congruent to any given angle.
Every segment has exactly one midpoint.
Postulate 9 Every angle, except a straight angle, has exactly one bisector. The sum of the measures of the angles with the same vertex on one side of a line and with no interior points in common is 180 degrees. The sum of the measures of all angles around a common vertex and with no interior points in common is 360 degrees. All right angles are congruent. Theorem 6 Two perpendicular lines form four congruent right angles.