已知直線
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⊥平面
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,直線m
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平面
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,有下面四個命題:
①
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∥
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⊥m;②
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⊥
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∥m;③
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∥m
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
⊥
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;④

⊥m
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∥
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其中正確命題序號是
.
試題分析:本題考查直線與平面垂直的判定與性質(zhì),直線

⊥平面

,
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∥
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⊥
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
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⊥m,①對;

⊥
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,
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⊥
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時直線

與平面
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可能平行,也可能線在面內(nèi),直線

與直線
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關(guān)系不確定,②錯;
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∥m,

⊥
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,
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m⊥
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
,③對;由

⊥m,不能得出

⊥

,故也不能有

∥

,④錯.
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
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
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
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
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
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的中點.
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
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;
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平面
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;
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,
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為

的中點.

(1)若

,求證:平面

平面

;
(2)點

在線段

上,

,若平面
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平面

,且

,求二面角

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在正方形

中,

是

的中點,

是側(cè)面

內(nèi)的動點且

//平面

,則

與平面

所成角的正切值得取值范圍為
.

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