连接AC AB=AD -> 绕A点旋转△ACD,使D点与B点重合,C点转至C' -> ∠ABC'=∠ADC,AC=AC',∠CAC'=∠BAD=90° 四边形ABCD中∠BAD=∠C=90° -> ∠ABC+∠ADC=180° -> ∠ABC+∠ABC'=180° -> C',B,C在同一直线上 AC=AC',∠CA...