解：?$(1) $?點(diǎn)?$A(-2，$??$0)，$??$B(-1，$??$0)，$??$C(-1，$??$2)$?關(guān)于?$y$?軸的對(duì)稱(chēng)點(diǎn)的坐標(biāo)
分別為?$A_{1}(2，$??$0)，$??$B_{1}(1，$??$0)，$??$C_{1}(1，$??$2)$?
∵直線?$l$?上點(diǎn)的橫坐標(biāo)都為?$3$?
∴點(diǎn)?$A_{1}(2，$??$0)，$??$B_{1}(1，$??$0)，$??$C_{1}(1，$??$2)$?關(guān)于直線?$l$?的對(duì)稱(chēng)點(diǎn)的坐標(biāo)
分別為?$A_{2}(4，$??$0)，$??$B_{2}(5，$??$0)，$??$C_{2}(5，$??$2)$?
?$(2) $?由題意知，點(diǎn)?$P_{1}$?的坐標(biāo)為?$(a，$??$0)，$?而點(diǎn)?$P_{2}$?與點(diǎn)?$P_{1}$?關(guān)于直線?$l$?對(duì)稱(chēng)
∴點(diǎn)?$P_{2}$?的坐標(biāo)為?$(6-a，$??$0)$?
∴?$PP_{2}$?的長(zhǎng)為?$6-a-(-a)=6$?
