Discovering the Sum of the Angles in a Triangle
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This activity will allow students to discover that the sum of the measures of the interior angles of any triangle equals 180°.
 

Materials Needed

1/4 sheets of construction paper
       (3 for each student)
Scissors
Rulers
Pen, pencil, or markers

 

1.  Have students place each sheet of construction paper on top of the other and cut out 3 identical triangles of their own choosing.  Using different colors of paper will be helpful.

2.  Separate the triangles.

3.  Label the vertices on all three triangles with the same letters.

 

 

4.  Next, using a ruler, draw a straight line. 

5.  Place angle A on the line, making sure that side AC is aligned with the straight line. 

6.  Follow the same procedure for angle B, aligning side AB from the first triangle with side BA from the second triangle.

7.  Repeat again for angle C, aligning side BC from the second triangle with side CB from the third triangle.  Their diagram should now look like this:

 

8.  Now have the students look at angles A, B, and C where they are next to each other on the straight line.  They will notice that they form a straight angle = 180°.