Constructing+Lines+Lesson

**Lesson: Constructing Parallel and Perpendicular Lines with a Compass**
In the following lesson, students gain an understanding of line pairs, leading up to constructing parallel and perpendicular lines with a compass. The blue portions of this lesson come directly from the teacher text. The other tools (videos, files, links) were added to respond to the needs of my students. Please feel free to comment (Click Discussion) or enhance this lesson (click EDIT and go for it!).

**Building understanding of line pairs presentation:**
The following presentation can be used to build background/understanding with foundational concepts related to line pairs. The KeyNote and PowerPoint versions of the presentations are linked below.

PLay first 30 seconds of video... media type="file" key="Line Pair Presentation.mov" width="300" height="300"

**Focus on Perpendicular and Parallel Li[[file:Line Pair Presentation.ppt]]nes:**
Before constructing parallel and perpendicular lines with a compass, students will review what they know about line pairs warm up for today's lesson by using the following video to identify parallel and perpendicular lines. Pause the video and allow students to circle the parallel and perpendicular lines on the whiteboard. **Use a different color for parallel and perpendicular.**

media type="youtube" key="ot4JlWhWwMw?version=3" height="345" width="560"
 * Embedded**


 * Link to Video:**
 * [|Parallel and Perpendicular Line Search Video]**

**Drawing and Constructing Perpendicular Lines**
1. Remind students that perpendicular lines intersect at one point. Perpendicular lines always make a right angle at the point where they intersect. 2. Have students sketch a line on a sheet of paper. 3. Have them sketch another line that looks perpendicular to the first line. 4. Remind students that to accurately construct perpendicular lines, they must use tools such as a compass and ruler. 5. Now have students draw a line segment about 3 inches long and label the endpoints A and B. 6. Have students set the point of the compass at point A and open the compass a width that is not all the way to point B, but beyond the middle of the segment. Ask students to draw an arc that extends from above the middle of the segment to below the middle of the segment. 7. Have students leave the compass the same width and set the point of the compass at point B. Have them draw a second arc that crosses their first arc both above and below the segment. Students should label the point where the arcs cross above the segment as point C and the point where the arcs cross below the segment as point D. 8. Be sure students use a ruler to draw line CD, which will be perpendicular to line segment AB. Students should label the point where line CD and line segment AB intersect as point E. 9. Have students use the protractor to measure angles CEA and CEB to check that each angle measures exactly 90°. Angles DEA and DEB will also measure exactly 90°.

http://www.mathopenref.com/constperpextpoint.html
 * Here is an interactive demonstration:**

media type="youtube" key="RXuXslsnsTA?version=3" height="345" width="420"
 * Here is a vide demonstration:**

For the link to this demonstration video, click here: [|Here!]

10. Remind students that parallel lines are always in the same plane, or twodimensional space. Parallel lines are always the same distance apart. They never intersect, or cross each other. 11. Have students sketch a line on a sheet of paper. 12. Have students sketch another line that looks parallel to the first line. 13. Remind students that to accurately construct parallel lines, they must use tools such as a compass and ruler. 14. Using the line CD and line segment AB they have drawn, have students set the compass width the same as the length of segment EB. Then have them extend the line segment to the right beyond point B to a point they will label as point F. By using the compass, they should make the length of segment BF the same as the length of segment EB. 15. Have students repeat the construction of a perpendicular line to create a second perpendicular line to line segment AF, following Steps 7–9. 16. Have students set the point of the compass at point E and open the compass a width that is not all the way to point F, but beyond point B. Ask students to draw an arc that extends from above point B to below point B. 17. Have students leave the compass the same width and set the point of the compass at point F. Have them draw a second arc that crosses their first arc both above and below point B. Label the point where the arcs cross above the segment as point G and the point where the arcs cross below the segment as point H. 18. Be sure students use a ruler to draw line GH, which will be perpendicular to line segment AF. 19. Ask: Which lines are parallel? Lines CD and GH are parallel. 20. Point out that when two lines are each perpendicular to another line or segment, as CD and GH are to segment AF, they are parallel to each other.
 * Drawing and Constructing Parallel Lines**

media type="youtube" key="7pmonTIWunk?version=3" height="345" width="420"
 * Video Example:**


 * Link to [|Video Example- Click Here]**

Next Steps: **Constructing Parallel and Perpendicular Lines to Make a Map**
21. Have students create a simple map by making parallel and perpendicular lines. Students can label lines with names. 22. Remind students to use a ruler and compass as they construct the parallel and perpendicular lines.

23. Ask students to identify parallel and perpendicular lines on their map.