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如图,点C为线段AB上一点,△ACM、△CBN是等边三角形.请你证明:(2)∠MFA=60°(3)△DEC为等边三角形

来源:学生作业帮 编辑:作业帮 分类:数学作业 时间:2024/07/19 00:15:16
如图,点C为线段AB上一点,△ACM、△CBN是等边三角形.请你证明:(2)∠MFA=60°(3)△DEC为等边三角形
∵∠NCB = 60°
∵∠MAC = 60°
∴MA∥NC
∴∠CEB=∠AMB
∵∠MCB = ∠MCN + ∠NCB = ∠MCN + 60°
∵∠ACN = ∠MCN + ∠ACM = ∠MCN + 60°
∴∠MCB = ∠ACN
∵△ACM、△CBN是等边三角形
∴AC = MC、CN=CB
∴△ACN≌△MCB
∴∠NAC = ∠BMC
∵∠CDN=∠DCA + ∠NAC = 60° + ∠NAC = 60° + ∠BMC = ∠AMB = ∠CEB
∵∠ECB = 60° = 180° - ∠DCE - ∠ACD = 180° - ∠DCE - 60° = 120° - ∠DCE
∴ ∠DCE = 60° = ∠ECB
∵ CB = CN
∴△ECB≌△DCN
∴CD = CE
∴∠CED = ∠CDE
∵∠DCE = 60°
∴∠CED = ∠CDE = (180° - 60°)/2 = 60°
∴△DEC = 为等边三角形
∴∠MFA = ∠FBA + ∠FAB = ∠ANC + ∠NAC = 180° - (∠DCA + ∠DCN)= 180° - 120°
∴∠MFA = 60°