Triangle Interior Angles: Quick Exploration
In the Geometry app below,
1) Use the POLYGON 
tool to construct triangle ABC.
2) Select the ANGLE 
tool. Then click anywhere inside the polygon.
3) Go to the Algebra view (click calculator icon upper left).
4) Calculate the sum of the measures of the interior angles of this triangle.
(Start at 0:38 in video at the bottom if you're unsure of how to do this in GeoGebra).
Keep going! There's a question below the app here.
tool to construct triangle ABC.
2) Select the ANGLE tool. Then click anywhere inside the polygon.
3) Go to the Algebra view (click calculator icon upper left).
4) Calculate the sum of the measures of the interior angles of this triangle.
(Start at 0:38 in video at the bottom if you're unsure of how to do this in GeoGebra).
Keep going! There's a question below the app here. 
Select the MOVE 
tool. Move any one (or more) of the triangle's vertices around.
What can we conclude about the sum of the measures of the interior angles of this triangle? Be specific in your response!
tool. Move any one (or more) of the triangle's vertices around.
What can we conclude about the sum of the measures of the interior angles of this triangle? Be specific in your response!