standard_description: Apply the area and perimeter formulas for rectangles in real world and mathematical problems. For example, find the width of a rectangular room given the area of the flooring and the length, by viewing the area formula as a multiplication equation with an unknown factor.
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
Teachers with a valid work email address can
click here to register or sign in
for free access to Student Response.
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?”


aligns: no