(2012•山东)如图,几何体E-ABCD是四棱锥,△ABD为正三角形,CB=CD,EC⊥BD.(Ⅰ)求证:BE=DE;(Ⅱ)若∠BCD=120°,M为线段AE的中点,求证:DM∥平面BEC.
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![(2012•山东)如图,几何体E-ABCD是四棱锥,△ABD为正三角形,CB=CD,EC⊥BD.(Ⅰ)求证:BE=DE;(Ⅱ)若∠BCD=120°,M为线段AE的中点,求证:DM∥平面BEC.](/uploads/image/z/3189695-23-5.jpg?t=%EF%BC%882012%26%238226%3B%E5%B1%B1%E4%B8%9C%EF%BC%89%E5%A6%82%E5%9B%BE%2C%E5%87%A0%E4%BD%95%E4%BD%93E-ABCD%E6%98%AF%E5%9B%9B%E6%A3%B1%E9%94%A5%2C%E2%96%B3ABD%E4%B8%BA%E6%AD%A3%E4%B8%89%E8%A7%92%E5%BD%A2%2CCB%3DCD%2CEC%E2%8A%A5BD%EF%BC%8E%EF%BC%88%E2%85%A0%EF%BC%89%E6%B1%82%E8%AF%81%EF%BC%9ABE%3DDE%EF%BC%9B%EF%BC%88%E2%85%A1%EF%BC%89%E8%8B%A5%E2%88%A0BCD%3D120%C2%B0%2CM%E4%B8%BA%E7%BA%BF%E6%AE%B5AE%E7%9A%84%E4%B8%AD%E7%82%B9%2C%E6%B1%82%E8%AF%81%EF%BC%9ADM%E2%88%A5%E5%B9%B3%E9%9D%A2BEC%EF%BC%8E)
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