1-4 Segments, Rays, Parallel Lines, and Planes

1. 1-4 Segments, Rays, Parallel Lines, and Planes Objectives: • Define line segments and rays • Properly name line segments and rays • Identify parallel lines and skew lines

2. Line Segments B A • A line segment is part of a line containing two endpoints and all points between them. • Unlike lines, which extend forever in both directions, line segments have a definite beginning and end • A line segment is named with the endpoints AB or BA

3. Rays • A ray is part of a line that consists of one endpoint and all points of the line extending in one direction • Name a ray using the endpoint first and then another point on the ray • When naming, make sure the arrow points away from the endpoint. B A AB , not BA

4. Rays, continued • Are these two rays the same? B AB A B A BA • No • Different endpoints • Extend in different directions

5. Opposite Rays • Are two collinear rays with the same endpoint • Always form a line J K L KJ and KL are opposite rays

6. Parallel Lines • Lines that • Never intersect • Extend in the same directions • Coplanar

7. Skew lines Lines that: • Never intersect • Are noncoplanar • Extend in different directions

8. Parallel Planes • Parallel planes are planes that never intersect • Example: the purple planes in the above illustration • A line and plane that never intersect are also parallel

9. Learning Check and Summary • Which of the following has no endpoints? • Ray, Line Segment, Line • Which of the following has two endpoints? • Ray, Line Segment, Line • Which of the following has one endpoint and extends in one direction? • Ray, Line Segment, Line • Which of the following extend in the same direction? • Parallel lines, skew lines • Which of the following extend in different directions? • Parallel lines, skew lines

10. Exercises • P. 13-15 All • P. 253 All • P. 255 All