1. 1-3 Collinearity and assumptions

2. . . . . . Collinear: Points that are on the same line.
Noncollinear: Points NOT on the same line. . . . . .

3. Draw one diagram with the following conditions:
A, B, and C are collinear
A, D, and E are collinear
B, C, and D are noncollinear

4. Betweenness: In order for us to say a point is
between two other points, ALL three points
must be collinear.
______ is between A and B.

5. Triangle Inequality Theorem:
The sum of the lengths of any two sides of a triangle
are greater than the length of the third. 3 5 4
3 + 4 > 5
4 + 5 > 3

6. General rules to follow when getting information from a diagram
You Should Assume
You Should NOT Assume
Straight lines and Angles
Right Angles
Collinearity of Points
Congruent Segments
Betweeness of Points
Congruent Angles
Relative Position of Points
Relative size of segments and angles

7. What should we assume about the given diagram? Do Assume Do Not AssumeC B A
Do Assume
Do Not Assume
, are straight lines
is a right angle
is a straight angle
C, D, and E are noncollinear
C is between B and E
is an obtuse angle
D is to the right of C
is longer than