Download Lesson 1.2

Lesson 1.2
Use segments and
congruence
Objective
• Use segment postulates to identify congruent
segments.
Standard
• 1.0 – Students demonstrate understanding by
identifying and giving examples of undefined
terms, axioms, theorems, and inductive and
deductive reasoning.
Academic Language
Postulate or axiom
• A rule that is accepted without
proof
Postulate 1
• The points on a line can be
matched one to one with
real numbers
Coordinate
• the real number that corresponds to a point
Points
A
B
X1
X2
Coordinates
Distance
• The absolute value of the difference of 2
points A and B, written as AB
A
AB
X1
B
X2
AB  x2  x1
Example 1
What is the distance between points S and T?
S
T
2
5.4
Indy Practice
What is the distance between points A and B?
A
B
-4
7
Adding Segment Lengths
• When 3 points are collinear, you can say that
one point is between the other two.
Example
A
D
B
C
E
F
Which point is between? Why?
Postulate 2 – Segment addition
Postulate
• If B is between A and C, then AB + BC = AC
• If AB + BC = AC, then B is between A and C
AC
A
B
AB
C
BC
The Real World
• The cities Lubbock, Tulsa, and St. Louis lie
approximately in a straight line on a map.
Tulsa is between Lubbock and St. Louis, 380
miles from Lubbock and 360 miles from St.
Louis. Find the distance from Lubbock, Texas
to St. Louis, Missouri
Indy Practice
1. Find the length of XZ
2. WY = 30. Can you use segment addition to
find the distance between W and Z? Explain
23
X
50
Y
W
Z
More Practice
• Find GH
36
F
21
G
H
Congruent Segments
• Line segments that have
the same length
Example
• Plot
J(-3, 4) K(2, 4)
L(1, 3)
M(1, -2)
Congruent?
Homework
• p.12 #1, 2, 3, 11, 13, 17, 21, 29, 33