Construction paper (for cutting out triangles)
Scissors
Rulers (optional, for measuring angles)
Protractors (optional, for additional measurement practice)
Student handout (available for download)
Introduction to the Activity:
Explain that students will explore and prove that the sum of the interior angles in any triangle is always 180 degrees.
Review the concept 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, large, small) from the construction paper.
Labeling and Cutting Angles:
Have students label or mark the interior angles of each triangle before cutting them off. This ensures they can identify the original angles after cutting.
Students should carefully cut out the angles from each triangle.
Investigating Angle Sums:
Instruct students to arrange the cut-out angles from each triangle along a straight line to measure their combined total.
Discuss whether the sum of the angles always equals 180 degrees, regardless of the triangle’s size or type.
Discussion and Reflection:
Engage students in a discussion about their findings. Did they find that the sum of the angles was always 180 degrees?
Reinforce the concept that the interior angles of a triangle always sum to 180 degrees, regardless of the triangle’s shape or size.
Optional Extension:
Introduce the concept of exterior angles and have students investigate how the exterior angles relate to the interior angles.
Use the protractors to measure the angles more accurately and discuss how the measurements confirm the sum of 180 degrees.
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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