共50条信息
如图,四棱柱\(ABCD-A_{1}B_{1}C_{1}D_{1}\)的底面\(ABCD\)是菱形,\(AC\cap BD=0\),\(A_{1}O⊥\)底面\(ABCD\),\(AB=2\),\(AA_{1}=3\).
\((1)\)证明:平面\(A_{1}CO⊥\)平面\(BB_{1}D_{1}D\);
\((2)\)若\(∠BAD=60^{\circ}\),求二面角\(B-OB_{1}-C\)的余弦值.
在如图所示的几何体中,四边形\(BB_{1}C_{1}C\)是矩形,\(BB_{1}⊥\)平面\(ABC\),\(A_{1}B_{1}/\!/AB\),\(AB=2A_{1}B_{1}\),\(E\)是\(AC\)的中点.
\((1)\)求证:\(A_{1}E/\!/\)平面\(BB_{1}C_{1}C\);
\((2)\)若\(AC=BC=2\sqrt{2}\),\(AB=2BB_{1}=2\),求二面角\(A—BA_{1}—E\)的余弦值.
如图\(1\),在四边形\(ABCD\)中,\(AC⊥BD\),\(CE=2AE=2BE=2DE=2\),将四边形\(ABCD\)沿着\(BD\)折叠,得到如图\(2\)所示的三棱锥\(A-BCD\),其中\(AB⊥CD\).
\((1)\)证明:平面\(ACD⊥\)平面\(BAD\);
\((2)\)若\(F\)为\(CD\)的中点,求二面角\(C-AB-F\)的平面角的余弦值.
如图,在四棱锥\(P\)\(\)\(ABCD\)中,底面\(ABCD\)是矩形,\(PA\)\(⊥\)平面\(ABCD\),\(PA\)\(=\)\(AD\)\(=4\),\(AB\)\(=2.\)以\(BD\)的中点\(O\)为球心,\(BD\)为直径的球面交\(PD\)于点\(M\).
\((1)\)求证:平面\(ABM\)\(⊥\)平面\(PCD\);
\((2)\)求直线\(PC\)与平面\(ABM\)所成角的正切值;
\((3)\)求点\(O\)到平面\(ABM\)的距离.
如图,在四棱锥\(S—ABCD\)中,底面梯形\(ABCD\)中,\(BC/\!/AD\),平面\(SAB⊥\)平面\(ABCD\),\(\triangle SAB\)是等边三角形,已知\(AC=2AB=4\),\(BC=2AD=2DC=2 \sqrt{5} \).
\((\)Ⅰ\()\)求证:平面\(SAB⊥\)平面\(SAC\);
\((\)Ⅱ\()\)求二面角\(B—SC—A\)的余弦值.
在正三棱锥\(P-ABC\)中,三条侧棱两两互相垂直,\(G\)是\(\triangle PAB\)的重心,\(E\),\(F\)分别为\(BC\),\(PB\)上的点,且\(BE︰EC=PF︰FB=1︰2\).
求证:\((1)\)平面\(GEF⊥PBC\);
\((2)EG⊥BC\),\(PG⊥EG\).
如图,四边形\(ABCD\)为正方形,\(PD\bot \)平面\(ABCD\), \(PD=\sqrt{3}AD\),\(AE\bot PC\)于点\(E\),\(EF/\!/CD\),交\(PD\)于点\(F\).
\((1)\)证明:平面\(ADE\bot \)平面\(PBC\);
\((2)\)求二面角\(D-AE-F\)的余弦值.
如图,\(\triangle ABC\)为等边三角形,\(D\),\(E\)是平面\(ABC\)同一侧的两点,且\(DA⊥\)平面\(ABC\),\(EB⊥\)平面\(ABC\),\(EB=2DA\).
\((1)\)求证:平面\(EDC⊥\)平面\(EBC\);
\((2)\)若\(∠EDC=90^{\circ}\),求直线\(EB\)与平面\(DEC\)所成角的正弦值.
如图,三棱锥\(P-ABC\)中,\(PB⊥\)底面\(ABC\),\(∠BCA=90^{\circ}\),\(PB=BC=CA=2\),\(E\)为\(PC\)的中点,\(M\)为\(AB\)的中点,点\(F\)在\(PA\)上,且\(2PF=FA\).
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