1 . 如图,在直角梯形ABCD中,AD//BC,
,当E、F分别在线段AD、BC上,且
,AD=4,CB=6,AE=2,现将梯形ABCD沿EF折叠,使平面ABFE与平面EFCD垂直.
(1)判断直线AD与BC是否共面,并证明你的结论;
(2)当直线AC与平面EFCD所成角为多少时,二面角A—DC—E的大小是60°.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/45acdbac251ca6b76a166c1242e71df9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/58cc90fee532e50d319081d571410421.png)
(1)判断直线AD与BC是否共面,并证明你的结论;
(2)当直线AC与平面EFCD所成角为多少时,二面角A—DC—E的大小是60°.
![](https://img.xkw.com/dksih/QBM/2010/4/6/1569691187535872/1569691192360960/STEM/0b252f9b-c573-4ca2-9bc3-2dcafbecd8b8.png?resizew=546)
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