![](https://www.ebk.net.cn/tikuimages/2/2017/400/shoutiniao6/cb7993a89c58fc12356129f0a6e9ddbc.png)
如图,\(PB\)为\(⊙O\)的切线,\(B\)为切点,直线\(PO\)交\(⊙\)于点\(E\)、\(F\),过点\(B\)作\(PO\)的垂线\(BA\),垂足为点\(D\),交\(⊙O\)于点\(A\),延长\(AO\)与\(⊙O\)交于点\(C\),连接\(BC\),\(AF\).
\((1)\)求证:直线\(PA\)为\(⊙O\)的切线;
\((2)\)试探究线段\(EF\)、\(OD\)、\(OP\)之间的等量关系,并加以证明;
\((3)\)若\(BC=6\),\(\tan ∠F= \dfrac {1}{2}\),求\(\cos ∠ACB\)的值和线段\(PE\)的长.