1、80°或50°或20°.
2、40.
3、∵ AD平分∠BAC,DC ⊥ AC,
DE ⊥ AB
∴ DC = DE.
∵ AC = BC,∠C = 90°,
∴ ∠B = ∠CAB = 45°(等边对等角).
∵∠DEB = 90°,
∴ ∠EDB = 45°.
∴ BE = DE(等角对等边).
∴ BE = DE = CD.
4、∵ ∠ACD = ∠ADC,
∴ AC = AD(等角对等边).在Rt△ABC和Rt△AED中,
∵ ∠ABC = ∠AED = 90°,AB = AD,
∴ Rt△ABC ≌ Rt△AED. ∴ BC = ED.
5、连接BD.
∵ AB = AD,
∴ ∠ABD = ∠ADB(等边对等角).
∵ ∠ABC = ∠ADC,
∴ ∠ABC - ∠ABD = ∠ADC - ∠ADB,即∠CBD = ∠CDB.
∴ BC = DC(等角对等边).
∴ △ABC ≌ △ADC.
∴ ∠BAC = ∠DAC,即AC平分∠BAD.
6、∵ △ABC是等边三角形,
∴ ∠CAB = ∠ABC = ∠ACB = 60°(等边三角形的各角都等于60°).
∵ AB ⊥ DE,BC ⊥ EF,AC ⊥ FD,
∴ ∠BAE = ∠CBF = ∠ACD = 90°.
∴ ∠ABE = ∠BCF = ∠DAC = 30°.
∴ ∠E = ∠F = ∠D = 60°.
∴△DEF是等边三角形(三个角都相等的三角形是等边三角形).