Reasoning about Angles (Part 2)
10 min
Narrative
In this Warm-up, students practice identifying obtuse angles in an image. They may, for instance, rely on the symmetry of the figure or on a grouping strategy, or otherwise scan the figure in a methodical way.
Launch
- Groups of 2
- “How many angles do you see? How do you see them?”
- Display the image.
- 1 minute: quiet think time
Teacher Instructions
- Display the image.
- “Discuss your thinking with your partner.”
- 1 minute: partner discussion
- Record responses.
Student Task
How many angles do you see in the folded paper heart?
Sample Response
Sample responses:
- I see 10 points around the edge of the heart. Each point is the vertex of an angle, so there are 10 angles.
- I see the heart has 10 straight sides. Each side-by-side pair of sides forms an angle, so there are 10 angles.
- I see 8 obtuse angles around the outer edge of the heart (4 on the left and 4 on the right) and 2 in the middle (on either side of the center line). I also see 2 acute angles at the bottom of the heart (on either side of the center line).
Synthesis
- “How did you make sure all the angles are accounted for?”(I put a mark through them or numbered them.)
- “How many obtuse angles are in this image?” (10)
- Label each obtuse angle with reasoning from students.
- Consider asking:
- “Who can restate in different words the way _____ saw the angles?”
- “Did anyone see the angles the same way but would explain it differently?”
- “Does anyone want to add an observation to the way _____ saw the angles?”
Standards
Addressing
- 4.G.1·Draw points, lines, line segments, rays, angles (right, acute, obtuse), and perpendicular and parallel lines. Identify these in two-dimensional figures.
- 4.G.A.1·Draw points, lines, line segments, rays, angles (right, acute, obtuse), and perpendicular and parallel lines. Identify these in two-dimensional figures.