如图,在三棱锥P-ABC中,PA⊥平面ABC,AB⊥AC,D、E、F分别是棱PA、PB、PC的中点,连接DE,DF,EF.
(1)求证:平面DEF∥平面ABC;
(2)若PA=BC=2,当三棱锥P-ABC的体积的最大值时,求二面角A-EF-D的平面角的余弦值.
考点分析:
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