Download Section 1.2

Quick Warm-Up
• Identify an
angle, segment,
ray, line, and
point in the
figure.
E
G
H
D 2
F
REVIEW
• How many different
angles can be named in
the figure? Name them.
A
B
V
C
Section 1.2
Measuring Length
Unit 1
The length of a segment
• Number Line:
– A line that has
been set up to
correspond with
the real
numbers.
A
• Coordinate of a Point
– A real number
– In the figure, -3 is the
coordinate of the point A,
and 4 is the coordinate of
the point B
B
DEFINITION:
Length of AB
• Let A & B be points on a number line, with
coordinates a and b. Then the measure of AB,
which is called its length, is:
Example
• Find the measures (lengths) of MN, NP, & MP on the
number line below.
M
N
P
Unit Length
• The distance from 0 to 1 on a ruler
• Most common unit lengths are inches and
centimeters.
0
1
2
3
4
Congruent Segments
• Congruent figures are
figures that are the same
size & shape.
• If you move one onto the
other, they will match
perfectly.
• Tick marks are used to show
which segments are
congruent
• The symbol for congruence
is:
• “XY = YZ” is read as
“Segment XY is congruent
to Segment YZ”
Name all congruent
segments
SEGMENT CONGRUENCE
POSTULATE
• If 2 segments have the same length
as measured by a fair ruler, then the
segments are congruent. ALSO, if 2
segments are congruent, then they
have the same length as measured
by a fair ruler.
What does that mean??
• If XY = YZ, then ___________________
• If XY = YZ, then _____________________
SEGMENT ADDITION
POSTULATE
• If point R is between points P and Q
on a line, then PR + RQ = PQ.
P
=
R
+
Q
Examples
• Point A is between points M and B on MB.
Sketch each figure & find the missing lengths.
– MA = 30
– MA = 15
– MA = ____
AB = 15
AB = ____
AB = 13.3
MB = _____
MB = 100
MB = 29.6
EXAMPLES
• Find the indicated value
– PR = 25
x = _____
– PQ = 25
PR = ______
P
Q
2x
P
R
3x
Q
R
5x
– PQ = 25
PR = ______
P
3x
Q
2x+1
R
x