[i][b]Background[/b][/i][br]You probably already know that a triangle is a shape having three sides.[br]Are there any other attributes or features that all triangles have in common?[br][br][b]Step 1. Collect Data[br][/b]Use the MOVE tool [icon]https://tube.geogebra.org/images/ggb/toolbar/mode_move.png[/icon] to move any of the corners of the triangle making a new triangle.[br][br]Enter the angle size in degrees for each of the interior angles in your new triangle into a Data Table.[br][br]Make two more different triangles and enter their interior angles into a Data Table.[br][br][b][i]Data Table[/i][/b]          Angle ABC         Angle BCA           Angle CAB[br][br][u]Triangle #1                                                                                      [br][/u][br][u]Triangle #2                                                                                      [br][/u][br][u]Triangle #3                                                                                      [br][/u][br][b][br]Step 2. Analyze the Data[br][/b]Look at the sum of the interior angles for each triangle.  Do you see a pattern?[br][br][b]Conclusions[/b][br]So, besides having three sides, what is another attribute of all triangles?[br][br]Turn on the [i]View Angle Calculator[/i].  Now move the corner points and see if your conclusion seems to be true.