Drawing Triangles (Part 2)
5 min
Teacher Prep
Setup
Narrative
The purpose of this Warm-up is to remind students that a compass is useful for transferring a length in general, and not just for drawing circles. As students discuss answers with their partners, monitor for students who can clearly explain how they can use a compass to compare the length of the third side.
Launch
Arrange students in groups of 2. Give students 2 minutes of quiet work time followed by time to discuss their answers with their partner. Follow with a whole-class discussion. Provide access to geometry toolkits and compasses.
Student Task
- Draw a 40∘ angle.
-
Use a compass to make sure both sides of your angle have a length of 5 centimeters.
-
If you connect the ends of the sides you drew to make a triangle, is the third side longer or shorter than 5 centimeters? How can you use a compass to explain your answer?
Sample Response
- See image.
-
- Shorter. Sample reasoning: The third side is shorter than 5 cm. I know this because I can use my compass that is set to a radius of 5 cm and place it at the end of one of the two sides. When I draw another circle, the end of the other side of the angle is inside that new circle, so the distance between the two ends must be less than 5 cm.
Activity Synthesis (Teacher Notes)
The purpose of this discussion is for students to share their observations and reasoning about using a compass to draw a triangle. Ask previously identified students to share their responses to the final question. Display their drawing of the angle for all to see. If not mentioned in students’ explanations, demonstrate for all to see how to use the compass to estimate the length of the third side of the triangle.
Standards
- 7.G.2·Draw (freehand, with ruler and protractor, and with technology) geometric shapes with given conditions. Focus on constructing triangles from three measures of angles or sides, noticing when the conditions determine a unique triangle, more than one triangle, or no triangle.
- 7.G.A.2·Draw (freehand, with ruler and protractor, and with technology) geometric shapes with given conditions. Focus on constructing triangles from three measures of angles or sides, noticing when the conditions determine a unique triangle, more than one triangle, or no triangle.
15 min
15 min
Knowledge Components
All skills for this lesson
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Drawing Triangles (Part 2)
5 min
Teacher Prep
Setup
Narrative
The purpose of this Warm-up is to remind students that a compass is useful for transferring a length in general, and not just for drawing circles. As students discuss answers with their partners, monitor for students who can clearly explain how they can use a compass to compare the length of the third side.
Launch
Arrange students in groups of 2. Give students 2 minutes of quiet work time followed by time to discuss their answers with their partner. Follow with a whole-class discussion. Provide access to geometry toolkits and compasses.
Student Task
- Draw a 40∘ angle.
-
Use a compass to make sure both sides of your angle have a length of 5 centimeters.
-
If you connect the ends of the sides you drew to make a triangle, is the third side longer or shorter than 5 centimeters? How can you use a compass to explain your answer?
Sample Response
- See image.
-
- Shorter. Sample reasoning: The third side is shorter than 5 cm. I know this because I can use my compass that is set to a radius of 5 cm and place it at the end of one of the two sides. When I draw another circle, the end of the other side of the angle is inside that new circle, so the distance between the two ends must be less than 5 cm.
Activity Synthesis (Teacher Notes)
The purpose of this discussion is for students to share their observations and reasoning about using a compass to draw a triangle. Ask previously identified students to share their responses to the final question. Display their drawing of the angle for all to see. If not mentioned in students’ explanations, demonstrate for all to see how to use the compass to estimate the length of the third side of the triangle.
Standards
- 7.G.2·Draw (freehand, with ruler and protractor, and with technology) geometric shapes with given conditions. Focus on constructing triangles from three measures of angles or sides, noticing when the conditions determine a unique triangle, more than one triangle, or no triangle.
- 7.G.A.2·Draw (freehand, with ruler and protractor, and with technology) geometric shapes with given conditions. Focus on constructing triangles from three measures of angles or sides, noticing when the conditions determine a unique triangle, more than one triangle, or no triangle.