[问答题]
Let $f(x)=\sin x-\sqrt{3} \cos x, 0 \leq x \leq 2 \pi$ .
The following diagram shows the graph of f .
The curve crosses the x -axis at A and C and has a maximum at point B .
1. Find the exact coordinates of A and of C .
2. Find $f^{\prime}(x) $.
3. Find the coordinates of B .
