共50条信息
如图,\(P\)为平行四边形\(ABCD\)所在平面外一点,\(M\)、\(N\)分别为\(AB\)、\(PC\)的中点,平面\(PAD∩\)平面\(PBC=l\).
\((1)\)求证:\(BC/\!/l\);
\((2)MN\)与平面\(PAD\)是否平行?试证明你的结论.
如图所示,在三棱锥\(P\)\(\)\(ABQ\)中,\(PB\)\(⊥\)平面\(ABQ\),\(BA\)\(=\)\(BP\)\(=\)\(BQ\),\(D\),\(C\),\(E\),\(F\)分别是\(AQ\),\(BQ\),\(AP\),\(BP\)的中点,\(AQ\)\(=2\)\(BD\),\(PD\)与\(EQ\)交于点\(G\),\(PC\)与\(FQ\)交于点\(H\),连接\(GH\).
\((1)\)求证:\(AB\)\(/\!/\)\(GH\);
\((2)\)求二面角\(D-\)\(\)\(GH\)\(\)\(-E\)的余弦值.
如图,矩形\(ABCD\)所在平面与三角形\(ECD\)所在平面相交于\(CD,AE\bot \)平面\(ECD\), \(2AE=AB=DE=2\),点\(M\)在线段\(AE\)上,\(N\)为线段\(CD\)的中点.
\((1)\)证明\(AB\bot \)平面\(ADE\);
\((2)\)若\(M\)为\(AE\)中点,求平面\(BDM\)与平面\(BNE\)所成锐二面角的余弦值;
\((3)\)若\(EN/\!/\)平面\(BDM\),求\(MN\)的长.
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