Lines and line segments can be measured and named using points labeled with letters. Lines extend indefinitely while line segments have distinct endpoints. Two line segments that intersect form angles, with the point of intersection called the vertex. Angles are named using the vertex letter in the middle. A right angle measures 90 degrees and is formed by perpendicular lines or line segments. Acute angles are less than 90 degrees while obtuse angles are greater than 90 degrees. Parallel lines never intersect even if extended indefinitely.

1. Lines and Angles

2. Lines are everywhere…

3. Line segments can be measured from beginning to end. A B We mark a line segment with points Those points are labeled with letters We can name this line segment either: AB BA

4. Lines vs. Line Segments Lines are different from line segments. We can see the beginning and ending of a line segment. Lines extend on forever To show the difference between a line and a line segment we use arrows instead of points A B We name a line by showing the arrows: AB

5. A B D C Two line segments are shown here AB CD

6. When lines or line segments meet… A B D C They intersect to form angles…

7. The point at the intersection is called the vertex. E A D B When we name the angle, the vertex must be in the middle C

8. The point at the intersection is called the vertex. AED E A D B When we name the angle, the vertex must be in the middle or C DEA Point E, the vertex, is always in the middle

9. X Notice any angles? Y A C P BAC XYZ PQR JHI Q Z R B J I Name these angles… H

10. A B D C When 2 line segments meet to form a 90° angle they called perpendicular line segments

11. A 90° 90° 90° 90° B D C Perpendicular lines intersect to form a 90° angle also referred to as a right angle. You can check if the angle right by holding up a piece of notebook paper.

12. Perpendicular A 90° B D C Where do we see right angles?

13. Perpendicular A B D C Where do we see right angles?

14. Let’s Look at the Strata Center again… Notice many perpendicular lines? Not quite 90° A A Smaller than 90° again. B B D D C C

15. A A B B D D C C

16. A A B B D D C C

17. Acute Angle = Less than 90° A A B B D D C C Both of these angles are smaller than 90° Angles smaller than 90° are called acute

18. What about angles larger than 90°?

19. What about angles larger than 90°? Angles larger than 90° are called obtuse Notice all of the extra room?

20. If you extend these two lines segments will they ever touch? Right, if they did what might happen?

21. When two line segments on the same plane never touch they are called Parallel Lots of parallel lines

22. Do these lines intersect? But, if you extend them outward, would they intersect? Are these lines parallel? No, but actually they are. It’s just the angle of the picture.

23. Examples of Parallel Lines