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如图,在△ABC中,D,E分别是AB,AC的中点,若DE=5,则BC的长是 .
如图,在△ABC中,D,E分别是AB,AC的中点,若DE=5,则BC的长是
.
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如图,图①是一块边长为1,周长记为P
1的正三角形纸板,沿图①的底边剪去一块边长为
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n-1等于( )
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A.
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B.3-
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+
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