The number of common points in the two angles marked in Fig. 2.19 is ____.

1
Think of “common points” as points that lie in both angles at the same time.
Write it step by step:
\(\text{Common points} = \text{points in both angles}\)
\(\text{Vertex of both angles} = A\)
\(\text{Arms do not overlap}\Rightarrow \text{no other shared point}\)
\(\therefore \text{Number of common points} = 1\)