As you can see the point C is between A and point B, hence AC + CB = AB. One thing to remember here is that point C can be anywhere between the point A and B, in that case, the answer will remain be the same AB. For instance:
A --- C -------------B
Again, AC + CB = AB.
2. By inference:
If the point C is between points A and B, it means that the point C lies on the line AB; if point C were not on the line AB, it will not be between points A and B. Hence, you can infer that AB is a line and point C lies on it and is between points A and B.
