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如图,四棱锥P-ABCD中,底面ABCD为平行四边形,∠DAB=60°,AB=2AD,PD⊥底面ABCD.
(Ⅰ)证明:PA⊥BD;
(Ⅱ)若PD=AD,求二面角A-PB-C的余弦值.
考点分析:
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=(
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,则∠C=
.
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