如图,四棱锥P-ABCD中,底面ABCD为矩形,PA⊥底面ABCD,PA=AB=根号2,点E是棱PB的中点若AD=1,求二面角B-EC-D的平面角的余弦值建议用向量法来做,
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![如图,四棱锥P-ABCD中,底面ABCD为矩形,PA⊥底面ABCD,PA=AB=根号2,点E是棱PB的中点若AD=1,求二面角B-EC-D的平面角的余弦值建议用向量法来做,](/uploads/image/z/5481253-37-3.jpg?t=%E5%A6%82%E5%9B%BE%2C%E5%9B%9B%E6%A3%B1%E9%94%A5P-ABCD%E4%B8%AD%2C%E5%BA%95%E9%9D%A2ABCD%E4%B8%BA%E7%9F%A9%E5%BD%A2%2CPA%E2%8A%A5%E5%BA%95%E9%9D%A2ABCD%2CPA%3DAB%3D%E6%A0%B9%E5%8F%B72%2C%E7%82%B9E%E6%98%AF%E6%A3%B1PB%E7%9A%84%E4%B8%AD%E7%82%B9%E8%8B%A5AD%3D1%2C%E6%B1%82%E4%BA%8C%E9%9D%A2%E8%A7%92B-EC-D%E7%9A%84%E5%B9%B3%E9%9D%A2%E8%A7%92%E7%9A%84%E4%BD%99%E5%BC%A6%E5%80%BC%E5%BB%BA%E8%AE%AE%E7%94%A8%E5%90%91%E9%87%8F%E6%B3%95%E6%9D%A5%E5%81%9A%2C)
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