Section 1.2 – Measuring Length

Number line – a line that has been set up to correspond with the real numbers.

A

B

C

4

The coordinate of a point on the number line is a real number.

Ex] -1 is the coordinate of point A and 4 is the coordinate of point C

Length of : Let A and B be points on a number line, with coordinates a and b. Then the measure of , which is called the length, is | a – b | or | b – a |.

The measure or length of is written as m or more commonly as just AB.

Ex] in the example above AB = | 4 – (-1) | = 5

** Remember that length is ALWAYS a POSITIVE number.**

Congruent Segments

Congruent figures are figures that are the same size and shape.

The symbol for congruence is .

is read as “segment AB is congruent to segment BC.” In geometry, tick marks are used to show which segments are known to be congruent.

If 2 segments have the same length as measured by a ruler, then the segments are congruent. If 2 segments are congruent, then they have the same length.

** Please remember that segments are congruent; measures (lengths) are equal. **

Look again at the first example. Notice that B is between A and C.

Segment Addition Postulate

If point B is between points A and C, then AB + BC = AC.