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20 0 2年 5月号问题解答(解答由问题提供人给出 )1 3 71 如图 ,凸四边形ＡＢＣＤ内接于⊙Ｏ ,延长ＡＢ、ＤＣ得交点Ｅ ,延长ＢＣ、ＡＤ得交点Ｆ .Ｍ、Ｎ各是ＡＣ、ＢＤ的中点 .且ＡＣ ＢＤ .求证 :ＭＮＥＦ =12 · ＡＣＢＤ-ＢＤＡＣ(安徽省怀宁江镇中学 黄全福 2 461 42 )
May 20, 2010 issue (provided by the problem provider) 1 3 71 As shown in the figure, the convex quadrangle ABCD is inscribed in ⊙O, the extended AB and DC are intersected by E, and the extended BC and AD are intersected by F .M. N and N are the midpoints of AC and BD. And AC BD. Proofs are: MNEF =12 · ACBD-BDAC (Huang Ning Jiang Zhen Middle School Huang Quanfu 2 461 42)