7.
如图,在三棱柱\(ABC-A_{1}B_{1}C_{1}\)中,\(AA_{1}⊥\)底面\(ABC\),\(AB⊥AC\),\(AC=AB=AA_{1}\),\(E\)、\(F\)分别是棱\(BC\),\(A_{1}A\)的中点,\(G\)为棱\(CC_{1}\)上的一点,且\(C_{1}F/\!/\)平面\(AEG\).
\((\)Ⅰ\()\)求\( \dfrac {CG}{CC_{1}}\)的值;
\((\)Ⅱ\()\)求证:\(EG⊥A_{1}C\);
\((\)Ⅲ\()\)求二面角\(A_{1}-AG-E\)的余弦值.