**Geometry Chapter 1.3 Segments and Their Measures**

**I) Vocabulary & Postulates:**

**A) theorems**: Rules that have been proven to be true.

Example: Triangle Sum Theorem: The sum of the measures of the interior angles of a triangle is 180 degrees.

**B) Postulates or Axioms**: Rules that we accept as true without proof.

**C) Between**- When 3 points are one a line, you may say that 1 point is between the others.

**D) Segment Addition Postulate or Partition Postulate**: If B is between point A and point C, then

AB + BC = AC

**E) Distance formula**: AB = √((x

_{1}- x

_{2})

^{2}+ (y

_{1}- y

_{2})

^{2})

this is derived from the pythagorean theorem, where the difference of the x's is represented by "a" and the difference of the y's is represented by "b" and AB = c so

a

^{2}+ b

^{2}= c

^{2}

**F) Congruent Segments**- Segments that have the same measure

Written:

Lengths are equal in length so: AB = CD

and

Segments are congruent so: line segment AB is congruent to line segment CD.