1.2 Ruler Postulates

1. 1-2 Ruler Postulates I Can: explain and give examples for the ruler postulate, the ruler placement postulate, and the segment addition postulate.

2. Bell Ringer Knowing that AB + BC = AC , solve for AC . 1. AB = 2, BC = 6 AC = 2 + 6, AC = 8 2. AB = 1, BC = 4 AC = 1 + 4, AC = 5 3. AB = 3, BC = 7 AC = 3 + 7, AC = 10 4. AB = 1, BC = 2 AC = 1 + 2, AC = 3 5. AB = 5, BC = 1 AC = 5 + 1, AC = 6

3. Rulers Measurement is an important part of geometry. You use measurement everyday. The measuring tool you use most often is a ruler. You can think of a ruler as a line with numbers on it.

4. Postulates Modern geometry has set some rules on how to use a ruler for geometric figures. The rules are called postulates . A postulate is a statement about geometric figures accepted as true without proof.

5. Absolute Value A number’s distance from zero on the number line.

6. Lesson Warm-Up Write the absolute value of each number on the number line.

7. Ruler Postulate: The points on a line can be placed in a one-to-one correspondence with real numbers so that 1. for every point on the number line, there is exactly one real number. 2. for every real number, there is exactly one point on the line. 3. the distance between any two points is the absolute value of the difference of the corresponding real numbers.

8. Ruler Postulate Example • A •B A corresponds to 0. B corresponds to 3. The distance between A and B is 3. Ruler Postulate: AB = 3 – 0 or 0 – 3 = 3 -5 5 10 -10

9. Ruler Placement Postulate Given two points, A and B on a line, the number line can be chosen so that A is at zero and B is a positive number.

10. Ruler Placement Postulate Example Given: A •A •B A = B = Think about what the ruler placement postulate says we can do… -5 5 10 -10 -5 5 10 -10

11. Segment Addition Postulate If B is between A and C, then AB + BC = AC.

12. Segment Addition Postulate Example •A •B •C A = B = C = -5 5 10 -10