1. The angles form a straight angle
2. A straight angle is defined to be 180 degrees
3. The three angles of any triangle always add to 180, as the diagram shows.
4. This is false. We need to add the three different angles A,B,C to get 180. Adding angle A to itself may not lead to 180. A+A = 180 only happens when angle A is a right angle (90 degree angle).