9.
如图,在四边形\(ABCD\)中,\(AB/\!/CD\),\(∠ABC=90^{\circ}\),\(AB=2BC=2CD\),对角线\(AC\)与\(BD\)相交于点\(O\),线段\(OA\)、\(OB\)的中点分别为\(E\)、\(F\).
\((1)\)求证:\(\triangle FOE\)≌\(\triangle DOC\);
\((2)\)求\(\sin ∠OEF\)的值;
\((3)\)若直线\(EF\)与线段\(AD\)、\(BC\)分别相交于点\(G\)、\(H\),求\(\dfrac{AB+CD}{GH}\)的值.