1. Def: Congruent Line Segments:
Congruent line segments are segments that are equal in measure.
Ex: A C D B If
Then AB = CD
Geometry Leeson: Undefined Terms, Lines, Line Segments

2. Def: Midpoint
The midpoint of a line segment is a point that divides the line segment into two congruent segments. A B M 1) 3) 5) 2) 4) 6)
Geometry Leeson: Undefined Terms, Lines, Line Segments

3. X A B 1)  2) Def: Line Bisector
The bisector of a line segment is a line that intersects the line segment at its midpoint. A B M P Q 1)  2) X
Geometry Leeson: Undefined Terms, Lines, Line Segments

4. Addition and Subtraction of Line Segments:
If several line segments belong to the same line, we can write addition and subtraction expressions using the names of these segments. R P S
Geometry Leeson: Undefined Terms, Lines, Line Segments

5. Opposite Rays
Opposite rays are two rays of the same line with a common endpoint and no other point in common.
In the figure below, AB and AC are opposite rays because points A, B, C are collinear and points B and C are on opposite sides of point A.
Geometry Leeson: Undefined Terms, Lines, Line Segments