7.
\((\)本小题满分\(10\)分\()\)
如图,\(CD\)为\(⊙O\)的直径,直线\(AB\)与\(⊙O\)相切于点\(D\),过\(C\)作\(CA⊥CB\),分别交直线\(AB\)于点\(A\)和\(B\),\(CA\)交\(⊙O\)于点\(E\),连接\(DE\),且\(AE=CD\).
\((1)\)如图\(1\),求证\(\triangle AED\)≌\(\triangle CDB\);
\((2)\)如图\(2\),连接\(BE\)分别交\(CD\)和\(⊙O\)于点\(F\),\(G\),连接\(CG\),\(DG\).
\(ⅰ)\)试探究线段\(DG\)与\(BF\)之间满足的等量关系,并说明理由;
\(ⅱ)\)若\(DG= \sqrt{2}\),求\(⊙O\)的周长\(.(\)结果保留\(π)\).
第\(20\)题图