已知:四棱锥P-ABCD,PA⊥平面ABCD,底面ABCD是直角梯形,∠A=90°,且AB∥CD,
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CD,点F在线段PC上运动.
(1)当F为PC的中点时,求证:BF∥平面PAD;
(2)设
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,求当λ为何值时有BF⊥CD.
考点分析:
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