options: Classify two-dimensional figures based on the presence or absence of parallel or perpendicular lines, or the presence or absence of angles of a specified size. Recognize right triangles as a category, and identify right triangles.

Recognize a line of symmetry for a two-dimensional figure as a line across the figure such that the figure can be folded along the line into matching parts. Identify line-symmetric figures and draw lines of symmetry.

Draw points, lines, line segments, rays, angles (right, acute, obtuse), and perpendicular and parallel lines. Identify these in two-dimensional figures.
problem_activity: 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
Activity
Display the image.
“Discuss your thinking with your partner.”
1 minute: partner discussion
Record responses.
Student Facing
How many angles do you see in the folded paper heart?
[IMG]
Student Response
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Activity 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?”


correct_option_index: 2