(7) Let $z \in \mathbf{C}$, and satisfy $|z-\mathrm{i}| \leqslant 1, A=\operatorname{Re}(z)\left(|z-\mathrm{i}|^{2}-1\right)$. Find $\max A$ and $\min A$.
(Answer: When $z=-\frac{\sqrt{3}}{3}+\mathrm{i}$, $\max A=\frac{2 \sqrt{3}}{9}$; when $z=\frac{\sqrt{3}}{3}+\mathrm{i}$, $\min A=-\frac{2 \sqrt{3}}{9}$ )