如图所示,矩形ABCD和梯形BEFC所在平面互相垂直,BE∥CF,∠BCF=∠CEF=90°,AD=,EF=2.(1)求证:AE∥平面DCF;(2)当AB的长为何值时,二面角A—EF—C的大小为60°?只看第二问,标答是这样的过点B作BH⊥EF交FE的延长
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![如图所示,矩形ABCD和梯形BEFC所在平面互相垂直,BE∥CF,∠BCF=∠CEF=90°,AD=,EF=2.(1)求证:AE∥平面DCF;(2)当AB的长为何值时,二面角A—EF—C的大小为60°?只看第二问,标答是这样的过点B作BH⊥EF交FE的延长](/uploads/image/z/5573029-13-9.jpg?t=%E5%A6%82%E5%9B%BE%E6%89%80%E7%A4%BA%2C%E7%9F%A9%E5%BD%A2ABCD%E5%92%8C%E6%A2%AF%E5%BD%A2BEFC%E6%89%80%E5%9C%A8%E5%B9%B3%E9%9D%A2%E4%BA%92%E7%9B%B8%E5%9E%82%E7%9B%B4%2CBE%E2%88%A5CF%2C%E2%88%A0BCF%3D%E2%88%A0CEF%3D90%C2%B0%2CAD%3D%2CEF%3D2.%281%29%E6%B1%82%E8%AF%81%3AAE%E2%88%A5%E5%B9%B3%E9%9D%A2DCF%3B%282%29%E5%BD%93AB%E7%9A%84%E9%95%BF%E4%B8%BA%E4%BD%95%E5%80%BC%E6%97%B6%2C%E4%BA%8C%E9%9D%A2%E8%A7%92A%E2%80%94EF%E2%80%94C%E7%9A%84%E5%A4%A7%E5%B0%8F%E4%B8%BA60%C2%B0%3F%E5%8F%AA%E7%9C%8B%E7%AC%AC%E4%BA%8C%E9%97%AE%2C%E6%A0%87%E7%AD%94%E6%98%AF%E8%BF%99%E6%A0%B7%E7%9A%84%E8%BF%87%E7%82%B9B%E4%BD%9CBH%E2%8A%A5EF%E4%BA%A4FE%E7%9A%84%E5%BB%B6%E9%95%BF)
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