∵GM=GC+MC=AD+MC, ∴AM=AD+MC. ······································································································· (4分) 方法四:
连接ME并延长交AD的延长线于点N, ∵∠MEC=∠NED, EC=ED, ∠MCE=∠NDE=90°, ∴△MCE≌△NDE. ∴MC=ND,∠CME=∠DNE. ··················································································· (2分) 由方法一知△EFM≌△ECM, ∴∠FME=∠CME, ∴∠AMN=∠ANM. ···································································································· (3分) ∴AM=AN=AD+DN=AD+MC. ················································································ (4分) (2)(本小问5分)
D 成立. ···················································· (1分) 方法一:延长CB使BF=DE,
连接AF,
E ∵AB=AD,∠ABF=∠ADE=90°,
∴△ABF≌△ADE, ∴∠FAB=∠EAD,∠F=∠AED. ··········· (2分)
C F B M ∵AE平分∠DAM, ∴∠DAE=∠MAE.
∴∠FAB=∠MAE, ∴∠FAM=∠FAB+∠BAM=∠BAM+∠MAE=∠BAE. ·················································· (3分) ∵AB∥DC, ∴∠BAE=∠DEA, ∴∠F=∠FAM, ∴AM=FM. ··············································································································· (4分) 又∵FM=BM+BF=BM+DE, ∴AM=BM+DE. ······································································································· (5分) 方法二:
设MC=x,AD=a.
由(1)知 AM=AD+MC=a+x. 在Rt△ABM中,
∵AM2 AB2 BM2,
∴(a x)2 a2 (a x)2, ······················································································ (3分)
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