3.
\((\)本小题满分\(10\)分\()\)如图,在矩形\(ABCD\)中,\(P\)为\(AD\)上一点,连接\(BP\)、\(CP\),过\(C\)作\(CE⊥BP\)于点\(E\),连接\(ED\)交\(PC\)于点\(F\).
\((1)\)求证:\(\triangle ABP\)∽\(\triangle ECB\);
\((2)\)若点\(E\)恰好\(BP\)的中点,且\(AB=3\),\(AP=k(0 < k < 3)\).
\(①\)求\(\dfrac{PF}{PC}\)的值\((\)用含\(k\)的代数式表示\()\);
\(②\)若\(M\),\(N\)分别为\(PC\)、\(EC\)边上的任意两点,连接\(NF\),\(NM\),当\(k=\sqrt{2}\)时,求\(NF+NM\)的最小值.