Unit 9 Contents

Adding the Angles of a Triangle

To investigate the angles in a triangle, complete the following questions.

2. Use a pencil and ruler to draw a triangle on a sheet of blank paper. Make sure the triangle covers at least one-fourth of the paper. Mark the vertices with dots as shown in the example.

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3. Measure the three angles of the triangle with your protractor. Write the angle measures inside the triangle. Cut out the triangle.

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4. Tear off the three angles as shown in the example.

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5. Place the three angles next to each other with the vertices and edges touching each other as shown.

6. Describe the angle that is formed when all three angles are placed together this way.
7. Add the angle measures of each angle in your triangle. What is the sum of the three angles?
8. Compare your results for Questions 6 and 7 with at least two other students' results. How do your results compare?