如图所示,在三棱锥\(P\)\(\)\(ABQ\)中,\(PB\)\(⊥\)平面\(ABQ\),\(BA\)\(=\)\(BP\)\(=\)\(BQ\),\(D\),\(C\),\(E\),\(F\)分别是\(AQ\),\(BQ\),\(AP\),\(BP\)的中点,\(AQ\)\(=2\)\(BD\),\(PD\)与\(EQ\)交于点\(G\),\(PC\)与\(FQ\)交于点\(H\),连接\(GH\).
\((1)\)求证:\(AB\)\(/\!/\)\(GH\);
\((2)\)求二面角\(D-\)\(\)\(GH\)\(\)\(-E\)的余弦值.