Perpendicular Lines
- Author:
- shayleeschutzman
- Topic:
- Straight Lines
Explanation: Students will create a line (GH) perpendicular to another line (AB) through point C. Point C will be on line AB. In order for something to be considered perpendicular, two lines must intersect at a 90-degree angle. This activity will allow students to create points, lines, and angles in order to create a perpendicular line. I would give my students this activity after we've already discussed angles and perpendicular lines. It would be given towards the end of the unit so they already know what a 90-degree angle looks like as well as what a perpendicular line looks like.
Instructions:
1. Create line AB with the line tool.
2. Create point C with the point tool. This point must be somewhere on the line AB.
3. Create a perpendicular line to line AB which intersects line AB at point C. This will be point D.
4. Create a circle with point C as the center using the circle tool. End the circle at point D. Hint: This will not pass through AB. Make sure this circle doesn't hit point A or B. Spread out points A, B, and C fairly equal. Don't make point D too far up from point C to avoid this from happening.
5. Create points E and F at the two intersections of the circle with the intersection tool. The two intersections should be on line AB.
6. Create a second circle with point E as the center. End the circle at point F.
7. Create a third circle with point F as the center. End the circle at point E.
**These two circles in steps 6 and 7 may go past points A and B which is okay.
8. Using the intersection tool again, create points G and H at the two intersections of the circles you just created.
9. Create line GH using the line tool.
10. Using the angle tool, create angle ACH. Hint: To create this angle correctly, click the angle tool, then click point A, then click point C, then click point H.
11. Using that angle, determine whether or not line GH is perpendicular to line AB at point C. To determine, drag line AB to the left and right or up and down to see if it stays perpendicular to line GH.
When you created points E and F, what did you notice about them in relation to point C?
What angle was created?
Did line GH stay perpendicular to line AB at point C when you tested it? If so, why?
Targeted Standard: Grade 4 Geometry: Draw and identify lines and angles, and classify shapes by properties of their lines and angles. CCSS.MATH.CONTENT.4.G.A.1.: Draw points, lines, line segments, angles (right, acute, obtuse), and perpendicular and parallel lines. Identify these in two-dimensional figures.