$解:?(1)?如圖①所示:$
$?AC+CE=\sqrt{{x}^2+25}+\sqrt{{x}^2-16x+65},?$
$當?A、??C、??E?在同一直線上,?AC+CE?最?。?
$?(2)?作點?N?關于?x?軸的對稱點?N',?連接?MN'?交?x?軸于點?P,?此時?PM+PN?的值最小,等于?MN',?$
$過點?M?作?y?軸的垂線交射線?N'N?于點?A,?如圖②所示.$
$?∵N(3,??2),?$
$?∴N'(3,??-2).?$
$設直線?MN'?得解析式為?y=kx+b,?$
$則?\{\begin{array}{l}{b=4}\\{3k+b=-2}\end{array},?$
$解得?\{\begin{array}{l}{k=-2}\\{b=4}\end{array}.?$
$?∴y=-2x+4.?$
$當?-2x+4=0?時,?x=2,?$
$?∴P(2,??0).?$
$在?Rt△AMN'?中,?AM=3,??AN'=6,?$
$?∴MN'=\sqrt{A{M}^2+AN{'}^2}=\sqrt{{3}^2+{6}^2}=3\sqrt{5}.?$
$?∴PM+PN?最小值為?3\sqrt{5}.?$