9.
如图\(1\),在\(\triangle \)\(ABC\)中,\(∠\)\(A\)\(=90^{\circ}\),将\(\triangle \)\(ABC\)折叠,使点\(A\)落在\(BC\)边上点\(D\)处,折痕为\(EF\)\((\)点\(E\)在\(AB\)上,点\(F\)在\(AC\)上\()\),且\(EF\)\(/\!/\)\(BC\),连接\(EC\)交\(DF\)于\(O\).
\((1)\)若\(AB\)\(=4\),\(AC\)\(=3\),求\( \dfrac{OD}{OF}\)的值;
\((2)\)如图\(2\),过\(D\)作\(DH\)\(⊥\)\(AC\)于\(H\),交\(CE\)于\(G\),求证:\(G\)是\(DH\)的中点;
\((3)\)若\(BD\)\(=\)\(nDC\),求\( \dfrac{AE}{AC}\)的值\(.(\)用含\(n\)的代数式表示\()\)