如图ABCD—A1B1C1D1是正四棱柱,侧棱长为1,底面边长为2,E是棱BC的中点.
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(1)求三棱锥D1—DBC的体积;
(2)证明BD1∥平面C1DE;
(3)求面C1DE与面CDE所成二面角的正切值.
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