如圖所示,若四邊形ABCD是一個等腰梯形,AB∥DC,M、N分別是DC、AB的中點,已知
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=a,
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=b,
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=c,試用a、b、c表示
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,
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,
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+
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.
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=-a+b+c,
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=
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a-b-
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c.
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+
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= a-2b-c.
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=
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+
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+
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=-a+b+c,
∵
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=
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+
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+
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,
∴
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=-
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,
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=-
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,
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=
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,
∴
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=
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a-b-
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c.
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+
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=
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+
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+
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+
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=2
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=a-2b-c.
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科目:高中數(shù)學(xué)
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如圖所示,在△ABC中,D、F分別是BC、AC的中點,
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=
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,
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=a,
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=b.
(1)用a、b表示向量
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、
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、
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、
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、
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;
(2)求證:B、E、F三點共線.
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在矩形
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中,
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,
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、
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分別為
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和
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的中點,在以
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、
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、
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、
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、
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、
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在
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;②若向量
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。
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中,已知
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是線段
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的中點,
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是
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的中點,若
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分別記為
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,則用
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表示
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.
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