如图\(1\),\(\triangle ABC\)内接于\(⊙O\),\(∠BAC\)的平分线交\(⊙O\)于点\(D\),交\(BC\)于点\(E(BE > EC)\),且\(BD=2 \sqrt {3}.\)过点\(D\)作\(DF/\!/BC\),交\(AB\)的延长线于点\(F\).
\((1)\)求证:\(DF\)为\(⊙O\)的切线;
\((2)\)若\(∠BAC=60^{\circ}\),\(DE= \sqrt {7}\),求图中阴影部分的面积;
\((3)\)若\( \dfrac {AB}{AC}= \dfrac {4}{3}\),\(DF+BF=8\),如图\(2\),求\(BF\)的长.