已知,在\(\triangle ABC\)中,\(∠BAC=90^{\circ}\),\(∠ABC=45^{\circ}\),点\(D\)为直线\(BC\)上一动点\((\)点\(D\)不与点\(B\),\(C\)重合\().\)以\(AD\)为边作正方形\(ADEF\),连接\(CF\)
\((1)\)如图\(1\),当点\(D\)在线段\(BC\)上时\(.\)求证:\(CF+CD=BC\);
\((2)\)如图\(2\),当点\(D\)在线段\(BC\)的延长线上时,其他条件不变,请直接写出\(CF\),\(BC\),\(CD\)三条线段之间的关系;
\((3)\)如图\(3\),当点\(D\)在线段\(BC\)的反向延长线上时,且点\(A\),\(F\)分别在直线\(BC\)的两侧,其他条件不变;
\(①\)请直接写出\(CF\),\(BC\),\(CD\)三条线段之间的关系;
\(②\)若正方形\(ADEF\)的边长为\(2 \sqrt {2}\),对角线\(AE\),\(DF\)相交于点\(O\),连接\(OC.\)求\(OC\)的长度.