1. DO NOW

3. Ruler Postulate The distance between any two points on the number line is the absolute value of the difference of their positions. AB = |a – b| a = coordinate of point A b = coordinate of point B

4. Find the length of the segments: 1. AC = 2. BD = 3. AD =4. BE = Solution: 1. AC = 92. BD = 9 3. AD = 114. BE = 13 -8-6137 A B CD E

5. Segment Addition Postulate If three points A, B and C are collinear and B is between A and C, then AB + BC = AC ABC

6. Example 1: If RS = 15 and ST = 9, then RT = ? Example 2. If ST = 15 and RT = 40, then RS = ? Solution: 1. RT = RS + ST = 15 + 9 = 24 Solution: 2. RT = RS + ST 40 = RS + 15 RS = 25 RST

7. Example 3: If DT = 60, find the value of x. Then find DS and ST: Solution: DS + ST = DT (2x – 8) + (3x – 12) = 60 5x – 20 = 60 simplify 5x = 80add 20 to each side x = 16divide each side by 5 DS = (2x – 8) = 2 (16) – 8 = 24 ST = (3x – 12) = 3 (16) – 12 = 36 DST 2x - 83x - 12

8. Measuring Angles An angle is formed by two rays with the same endpoint. This common endpoint is called the vertex. Angle can be named as: ABC, CBA, B, 1.

9. Measuring Angles Angles are measured in degrees. The measure of A is written as m A For example: m A = 80º. 80º

10. Angles classified by measure 1.Acute Angle: 0º < x < 90º 2.Right Angle: x = 90º 3.Obtuse Angle: 90º < x < 180º 4.Straight Angle: x = 180º

11. How do we measure angles ?? Angles are measured using protractors.

12. Using your protractors construct the angles measuring: 1.35 º2. 90 º 3. 105 º4. 180 º

13. Angle Addition Postulate If point B is in the interior of AOC, then m AOB + m BOC = m AOC A O C B

14. Example 1: m RST = 50º and m RSW = 125º. What is m TSW? Example 2: m DEG = 145º. What is m GEF? Solution 1. 75ºSolution 2. 35º S R T W D G F E

15. Concepts of congruent segments Segments that have the same measure are congruent segments. Symbol of congruence AB CD A B C D 1.7 cm

16. HW Section 1.2, pg. 18-19, #5-8, 16-19, 21, 22, 27-29.