Investigating the Triangle Sum Theorem
To investigate interior angles of a triangle:
Complete the following steps/questions.
1) Write a theory about the interior angles of a isosceles triangle.
2) Click and drag the vertices to form an isosceles triangle.
3) Record the interior angle measures of the triangle and state how you know it is isosceles.
4) Write an equation relating the interior angle measures of the triangle.
5) Repeat steps 1 thru 4 for a scalene and a right triangle.
6) What do you observe about the triangle's 3 interior angles?
7) Does your theory come true for each case? Why or why not?

1) Hit the Reset Construction button (in upper right hand corner).
2) Click and drag the vertices to create 3 types of triangles: an acute, an obtuse, and a right triangle.
3) Record the interior angle measures of the triangle for each case.
4) Write an equation relating the 3 interior angle measures for each case.
5) What do you observe about the triangle's three interior angles when the sliders are set to 180?
6) Does the Triangle Angle Sum Theorem hold true for each case? Be prepared to explain your answer.