(2001•安徽)如图1,AB、CD是两条线段,M是AB的中点,S
△DMC、S
△DAC、S
△DBC分别表示△DMC、△DAC、△DBC的面积.当AB∥CD时,则有S
△DMC=
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.
(1)如图2,M是AB的中点,AB与CD不平行时,作AE、MN、BF分别垂直DC于E、N、F三个点,问结论①是否仍然成立?请说明理由.
(2)若图3中,AB与CD相交于点O时,问S
△DMC、S
△DAC和S
△DBC三者之间存在何种相等关系?试证明你的结论.
考点分析:
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