1、3,△ABD ≌ △DCA,△ABC ≌ △DCB,
△ABE ≌ △DCE
2、AC = AD(或∠C = ∠D,或∠B = ∠E).
3、(A). 4、(D). 5、(B).
6、∵ ∠ADC = ∠BCD,∠1 = ∠2,
∴ ∠ADC - ∠1 = ∠BCD - ∠2,即∠BDC
= ∠ACD.在△ADC和△BCD中,
∵ ∠ADC = ∠BCD,DC = CD,
∠ACD = ∠BDC,
∴ △ADC ≌ BCD(ASA).
∴ AD = BC.
7、13 cm.
8、∵ ∠DBE = 90°,∠ABD + ∠DBE + ∠EBC = 180°,
∴ ∠ABD + ∠EBC = 90°,
∵ ∠A = 90°,
∴ ∠ABD + ∠D = 90°.
∴ ∠D = ∠EBC.在 △ABD和△CEB中,
∵ ∠D = ∠EBC,∠A = ∠C = 90°,AB = CE,
∴ △ABD ≌ △CEB(AAS).
9、5.6 cm
10、∵ ∠2 = ∠1,AC = AC,∠4 = ∠3,
∴ △ABC ≌ △ADC(ASA).
∴ AB = AD.在△ABE和△ADE中,
∵ AB = AD,∠2 = ∠1,AE = AE,
∴△ABE≌ △ADE(SAS).
∴ BE = DE.
11、BC = B′C′.
∵ AD ⊥ BC, A′D′⊥ B′C′,
∴ ∠ADB = ∠A′D′B′= 90°.又AB = A'B', AD = A'D',
∴ Rt△ABD ≌ Rt△A'B'D'(HL).
∴ ∠B = ∠B′.又AB = A′B′,BC = B′C′,
∴ △ABC ≌ △A′B′C′(SAS).
12、分割线如图(△ABG ≌ △DEH,△CBG ≌ △DFH).