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Classifying Triangles by Internal Angles
Students will be able to sort triangles based on features of their internal angles.
- Start off with a game of Simon Says. Direct your students to imitate you making three different angles with your arms: right angle (one at 90 degrees), an acute angle (one at less than 90 degrees), and an obtuse angle (one greater than 90 degrees).
- As you make your angle and the students imitate you, tell them the definition of each angle you make. For example, "Simon says make a right angle; this angles is at 90 degrees."
Explicit Instruction/Teacher modeling(10 minutes)
- Hand out and preview the Sorting Triangles worksheet and observe the shape labeled #9 in the shapes box.
- Have students review the angle categories, turn to a neighbor and share which category triangle #9 belongs in.
- Allow for students to determine that it is an obtuse triangle and place the number 9 on the proper section of the diagram where obtuse does not overlap with another category. Answer any clarifying questions.
Guided Practice(5 minutes)
- Repeat the process for another shape, but allow students to determine the proper placement of the shape number.
- Guide your students with leading questions as needed and answer any clarifying questions.
Independent working time(15 minutes)
- Have your students complete the remaining exercise on the Sorting Triangles worksheet.
- Inform students to cross off items that don't qualify for categorization (e.g., the quadrilaterals) to limit potential triangle choices.
- Students can focus on one angle type at a time (e.g., acute triangles) and cross off their choices as they go.
- Students can make a poster for one or both of the Thinking Deeper activities using pictures, words, and numbers.
- Show students three different types of triangles numbered 1, 2, and 3. Say a category (i.e., obtuse triangle, acute triangle, right triangle) and have them show a number with their fingers for the category the triangle belongs to.
- Choose students to share their rationale using some of the key terms from the lesson.
Review and closing(10 minutes)
- Review the answers as a class and allow for peers to assist with incorrect responses.
- Assign an exit ticket activity where students modify one of their choice of angles 6–8 so that they COULD be placed in one of the three diagram categories.