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Learn about postulates, theorems, ruler postulate, and segment addition postulate in geometry. Discover how to find lengths of segments and solve real-life examples involving algebra. Understand congruent segments and compare segments for congruence. Access homework exercises on pages 12-13.
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Do Now: Using the picture below, decide whether the statements are true or false.
Geometry 1.2: Use Segments and Congruence
Vocabulary • Postulate (Axiom): a rule in geometry that is accepted without proof. • Theorem: a rule that can be proved.
Ruler Postulate • The distance between two points A and B, written as AB, is the absolute value of the difference of the coordinates A and B.
Segment Addition Postulate • If B is between A and C, then AB + BC = AC.
Examples 1) Find the length of AC AC = AB + BC AC = 5 +14 AC =19 2) Find the length of BC BC = AC – AB BC = 38 – 17 BC = 21
Real-Life Example Distance from Lubbock to St. Louis is about 740 miles.
Examples Involving Algebra • Write an expression to represent the length of AC AC = AB + BC AC = x + 6 + 2x + 3 AC = 3x + 9 2) Find the value of x: 27 = 3x+9 -9 -9 18 = 3x • 3 x = 6
Congruent Segments • If line segments have the same length, then the segments are congruent. AB = CD AB CD
HOMEWORK Text p12-13: # 3, 6, 9, 13, 21-26