For IWB
Rounding issues with rounding to 0dp sorted by adding a slider incremented by 1degree.
1. Uncheck all and move points A, B at the point and angle C using the slider - to explore angles of triangle.
2. Check "Sum" to show angles add up to 180.
3. Check "Rule" to show rule.
4. Uncheck "Sum", check unknown to do some problem solving.
