Download Geometry: Section 1.3 Name:

Geometry: Section 1.3
Name:
Objective: To define collinear and noncollinear, betweenness of points, and to
learn the triangle inequality.
Colllinear points: Points are collinear if they lie on the same line.
Are two points always collinear?
Are three points always collinear?
Can four points be collinear?
Noncollinear points: Points which are not on the same line.
Betweenness of Points: B is between A and C if:
a) A, B, and C are collinear
b) AB + BC = AC
We write B is between A and C by writing A-B-C.
Three points can be collinear: AB + BC = AC or form the vertices of a triangle,
AB + BC > AC
Triangle Inequality: The sum of any two sides of a triangle is greater than
the third side.
C
C
b
A
c
<a<
a
5
a
B
_____
A
13
________ < a < ________
What facts can you assume from diagrams?
1) Collinearity and betweeness of points
2) Lines are straight
3) Whether a point is to the right or left of another
What facts can you NOT assume from diagrams?
1) Whether an angle is acute, right or obtuse
2) Whether angles are congruent.
3) Whether segments are congruent.
Homework: 1.3 pgs. 20-22 #3-7 all, 10-16 all
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