(2014•池州二模)如图,在六面体A1B1C1-ABDE中,平面A1B1C1∥平面ABDE,△A1B1C1是正三角形,
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(2014•池州二模)如图,在六面体A
1B
1C
1-ABDE中,平面A
1B
1C
1∥平面ABDE,△A
1B
1C
1是正三角形,四边形AA
1B
1B是直角梯形,AA
1⊥AB,四边形AEC
1A
1是正方形,四边形ABDE是等腰梯形,AB∥DE,AB=2AE=2DE=2.
(Ⅰ)证明:AB
1∥平面C
1DE;
(Ⅱ)求平面AB
1E与平面BB
1C
1D所成锐二面角的余弦值.