Example 3. Given points A, B and line l in the same plane, try to find a point P on l such that
$$
P A+P B \text { is minimal. }
$$
Slightly explained: Suppose A and B are on the same side of l, construct the symmetric point of A with respect to l as $\mathrm{A}^{\prime}$, connect $\mathrm{A}^{\prime} \mathrm{B}$ intersecting $\mathrm{l}$ at $\mathrm{P}$. Then $P$ is the desired point.