
如图,△ABC中,M是BC的中点,AD平分∠BAC,BD⊥AD,AB=12,MD=5,求AC的长
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解:延长BD,与AC交于点E
∵∠BAD = ∠EAD
AD = AD
∠ADB = ∠ADE = 90°
∴ △ADB≌△ADE
∴ AE = AB = 12
BD = DE
∵BM = CM
∴ DM = 1/2 EC
∴ EC = 2DM = 10
故:AC = AE+CE = 22
∵∠BAD = ∠EAD
AD = AD
∠ADB = ∠ADE = 90°
∴ △ADB≌△ADE
∴ AE = AB = 12
BD = DE
∵BM = CM
∴ DM = 1/2 EC
∴ EC = 2DM = 10
故:AC = AE+CE = 22
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