1. Let’s Get It Started . . .
Cut your drink stirrers into 3 UNEQUAL lengths and then form a triangle with them on your desktop.

2. Measuring Segments and Angles
Lesson 1-4
Measuring Segments and Angles

3. Ruler Postulate
The distance between two points is the absolute value of the difference between them. A B

4. Congruent Segments A B C D
Two segments with the same length are congruent. A B C D
The numbers (the measures are equal)
The figures (the segments are congruent)

5. Segment Addition Postulate
If 3 points A, B, and C are collinear and B is between A and C, then A B C

6. Betweenness A B C A B C A B C 8 10
Collinear: if one point is between the other two, two of the distances add to the third.
Non-collinear: three non-collinear points determine a triangle
Triangle Inequality Theorem: the sum of the distances of any two sides of a triangle is always greater than the third.
Ex: A triangle has sides of lengths 8 cm and 10 cm. What are possible lengths for the third side? A B C A B C A B C 8 10

7. Using the Segment Addition PostulateQ R S

8. Angles
Angle: formed by two rays sharing an endpoint (vertex).
Congruent Angles: angles with the same measure. Q 5 R
The numbers (the measures are equal) S A
The figures (the segments are congruent) 1 B 2 C D

9. Classifying Angles
Acute Obtuse Right Straight

10. Angle Addition PostulateB A O C B A B O C C A O

11. Using the Angle Addition PostulateB O C

12. Using the Angle Addition PostulateR S P T
reject

13. Using the Angle Addition PostulateB C
Find each angle. A O D