Key Concepts: Linear Measure and Precision

Line Segments

A Line segment is a part of a Line bounded by two endpoints. Unlike a Line, a segment has a definite length. The length of segment AB is written as AB (without the bar above).

Measuring Segments

• Use a ruler to find the distance between two points.
• The precision of a measurement depends on the smallest unit on the measuring tool.
• All measurements are approximations — the true value lies within a range determined by the precision.

Betweenness of Points

Point B is between points A and C if A, B, and C are collinear and AB + BC = AC. This is called the Segment Addition Postulate.

Congruent Segments

Two segments are congruent (≅) if they have the same length. Notation: AB ≅ CD means segment AB is congruent to segment CD.