Construction paper (for cutting out triangles)
Scissors
Glue or tape (for assembling)
Rulers (optional, for measuring angles)
Protractors (optional, for measuring angles)
Student handout (available for download)
Introduction to the Activity:
Explain that an exterior angle is formed when one side of a triangle is extended, creating a new angle outside the triangle.
Review the concept that the sum of the interior angles of a triangle is always 180 degrees and that a straight line equals 180 degrees.
Preparing the Triangles:
Distribute construction paper and scissors to each student or pair.
Instruct students to cut out multiple triangles of different sizes and types (acute, obtuse, etc.) from the construction paper.
Creating and Labeling Angles:
Have students extend one side of each triangle to create an exterior angle.
Mark and label the interior angles of each triangle, including the newly formed exterior angle.
Cutting and Comparing Angles:
Students should cut out the interior angles of each triangle.
Instruct students to line up the cut-out interior angles with the exterior angle to visually compare them.
Investigating the Relationship:
Guide students to observe and discuss how the sum of the two opposite interior angles equals the exterior angle.
Use the concept that the sum of the interior angles is 180 degrees and the sum of the exterior angle and the adjacent interior angle is also 180 degrees to explain why this is true.
Discussion and Reflection:
Discuss the findings with the students. Did they find that the exterior angle was equal to the sum of the two opposite interior angles in each case?
Reinforce the concept with visual examples and by referring to the provided student handout.
Optional Extension:
Challenge students to create additional triangles and explore how different types of triangles affect the relationship between exterior and interior angles.
Introduce the concept of adjacent angles and how they relate to exterior angles in more complex geometric figures.
Assessment:
Use the student handout to assess understanding and provide feedback on their work.
Review the answer key and teaching tips provided in the download to ensure accurate and effective teaching.
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