初三证明题....在线等 非常急~

在△ABC中，∠ABC=90°，AC=BC,直线MN过点C，且AD⊥MN，BE⊥MN
(1)当直线MN绕点C旋转到图1的位置时，求证：△ADC≌△CEB,DE=AD+BE
(2)当直线MN绕点C旋转到图2的位置时，求证:DE=AD-BE

(1)① ∵ ∠ADC = ∠ACB = 90 ,
∴ ∠CAD + ACD = 90 , ∠BCE + ∠ACD = 90 .
∴ ∠CAD = ∠BCE .
∵ AC = BC ,
∴ △ ACD ≌ △CBE ;
②∵ △ ADC ≌ △CED ,
∴ CE = AD , CD = BE .
∴ DE = CE + CD = AD + BE .

(2)∵ ∠ADC = ∠CEB = ∠ACB = 90 ,
∴ ∠ACD = ∠CBE .
∵AC=BC ,
∴ △ ACD ≌ △CBE .
∴ CE = AD , CD = BE .
∴ DE = CE-CD = AD-BE .