Linear Measure
Objective: (1)To measure segments and
determine accuracy of measurement.
(2) To compute with measures.
Definitions
• Line segment: A measureable part of a line that consists of
two points, called endpoints, and all of the points between
them.
• Precision: The precision of any measurement depends on
the smallest unit available on the measuring tool
• Betweeness of points:
• Between: For any two points A and B on a line, there is
another point C between A and B if and only if A, B, and C
are collinear and AC + CB = AB
• Constructions: A method of creating geometric figures
without the benefit of measuring tools. Generally, only a
pencil, straightedge, and a compass are used.
• Congruent: Having the same size and same shape.
Line Segments
• Consists of two
endpoints
• And all points in
between
• Has an infinite number
of points.
• Since it is finite, it has a
distance.
• Named by the
endpoints
– AB or BA
•
A
•
B
Symbols Review
AB
A
a
AB
Here’s a new one:
AB
Line AB
A or Point A
Line a
Segment AB
The Length of Segment AB
Betweeness of Points
• Point M is between
points P and Q if and
only if P, Q and M are
collinear & if:
PM + MQ = PQ
• Notice that M is
between but not in the
middle! There’s a
difference.
P
• •
M
•
Q
Finding the Distance
A
Find AB if AC = 19cm and
BC = 12cm
Since we don’t know what
AB is, we’ll say, AB = x
We also know:
AB+BC=AC … now replace
x + 12 = 19
-12 -12
x=7
x cm
B

12cm
C
19cm
Another way to find the distance
• Find x if:
AB = 5x+7, BC = 3x + 2
and AC = 33m
Plug in what you know
Also AB+BC=AC
5x + 7 + 3x + 2 = 33
8x + 9 = 33
-9 -9
8x = 24
C
3x + 2
B

33cm
5x + 7
A
Continued
8x = 24
8 8
x=3
Now, just in case you’re
asked to find AB or BC.
Replace the variable with
3
C
3x
911++2+2 2
3(3)
B

33cm
5x+++777
22
5(3)
15
A