如图,四边形\(ABCD\)是正方形,\(E\)是直线\(CD\)上的点,将\({\triangle }{ADE}\)沿\(AE\)对折得\({\triangle }{AFE}\),直线\(EF\)交边\(BC\)于点\(G\),连接\(AG\).
\((1)\)求证:\({\triangle }{ABG}\)≌\({\triangle }{AFG}\);
\((2)\)当\(DE\)是线段\(CD\)的一半时,请你在备用图中利用尺规作图画出符合题意的图形\((\)保留作图痕迹,不写作法\() \)
\((3)\)在\((2)\)的条件下,求\({∠}{EAG}\)的度数.