2020-01-03题目解析

题目6

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(1)

• 3AC = 2 AB -- > AC = (2/3) AB BC = (1/3) AB
• AB = (1/2) AB ; D 是 AB中点
• E 是 CB的中点
• DE = DC + CE = DC + (1/2) * BC = DC + (1/6) AB
• DC = DB - BC = (1/2) AB - (1/3) AB = (1/6) AB
• DE = (1/3) AB
• AB = 18
  (2)
• AD = (1/2) AB
• CB = (1/3) AB
• AD : CD = 3 : 2

题目4

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• EF = EB + BC + CF
• AB = (3/9) AD = (1/3) AD
• EB = (1/2) AB = (1/6) AD
• BC = (2/9) AD
• CD = (4/9) AD
• CF = (1/2) CD = (2/9) AD
• EF = (1/6 + 2/9 + 2/9) AD = (11/18) AD
• AD = 36

题目3

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• CD = AB - AD - CB = (1 - 1/4 - 1/3) AB = (5/12) AB
• CD = 5 cm
• BD = DC + CB = (5/12 + 1/4) AB = (8/12) AB = 8 cm