Chapter 3 Parallel and Perpendicular Lines LEARNING OBJECTIVES RECOGNIZE RELATIONSHIPS WITHIN LINES PROVE THAT TWO LINES ARE PARALLEL BASED ON GIVEN INFORMATION LESSON 3.6: PROVE THEOREMS ABOUT PERPENDICULAR LINES
Theorem 3.8 If two lines intersect to from a linear pair of congruent angles, then the two lines are perpendicular What does linear pair mean? If they are congruent what measure must they be? Ex. If 1 2 then g h 12 g h
Theorem 3.9 If two lines are perpendicular, then they intersect to form four right angles. If g h then 1, 2, 3, and 4 are right angles g h
GUIDED PRACTICE
Theorem 3.10 If two sides of two adjacent acute angles are perpendicular, then the angles are complementary. If BA BC, then 1 and 2 are complementary B A C 1 2
Check Point Given that ABC ABD what can you conclude about 3 and 4? CDB A 4 3
Theorem 3.11 – Perpendicular Transversal If a transversal is perpendicular to 1 of 2 // lines, then it is perpendicular to the other.
Theorem 3.12 – Lines Perpendicular Transversal In a plane, if two lines are perpendicular to the same line, then they are // to each other.
Distance from a Point to a Line The distance from a line to a point not on the line is the length of the segment ┴ to the line from the point. l A
Distance Between Parallel Lines Two lines in a plane are || if they are equidistant everywhere. To verify if two lines are equidistant find the distance between the two || lines by calculating the distance between one of the lines and any point on the other line.
EXAMPLE 4 Find the distance between two parallel lines SCULPTURE: The sculpture on the right is drawn on a graph where units are measured in inches. What is the approximate length of SR, the depth of a seat?
EXAMPLE 4 Find the distance between two parallel lines SOLUTION You need to find the length of a perpendicular segment from a back leg to a front leg on one side of the chair. The length of SR is about 18.0 inches. The segment SR is perpendicular to the leg so the distance SR is (35 – 50) 2 + (120 – 110) inches. d = The segment SR has a slope of 120 – 110 = – 50 – = 2 – 3. Using the points P(30, 80) and R(50, 110), the slope of each leg is 110 – 80 = – 30 = 3 2.
YOUR TURN Use the graph at the right for Exercises 5 and What is the distance from point A to line c? 6. What is the distance from line c to line d? 5. about about 2.2 ANSWER
YOUR TURN 7. Graph the line y = x + 1. What point on the line is the shortest distance from the point (4, 1). What is the distance? Round to the nearest tenth. (2, 3); 2.8 ANSWER
Homework Assignment Pg. 194 – 197 #2 – 10, 13 – 24, 26, 31, 35 – 38