1.2 Segments and Segment Addition

Notes

A segment $\overline{AB}$ is the part of a line between endpoints $A$ and $B$. Its length is written $AB$.

• A ray $\overrightarrow{AB}$ starts at $A$ and goes forever through $B$.
• Congruent segments have equal lengths: $\overline{AB} \cong \overline{CD}$ means $AB = CD$.
• Segment Addition Postulate: if $B$ is between $A$ and $C$, then $AB + BC = AC$.
• Example: $B$ is between $A$ and $C$, $AB = 2x + 1$, $BC = 3x$, $AC = 21$. Then $5x + 1 = 21$, so $x = 4$ and $AB = 9$.