共50条信息
如图,在三棱锥\(P-ABC\)中,\(PC⊥ \)底面\(ABC\),\(AB⊥BC \),\(D\),\(E\)分别是\(AB\),\(PB\)的中点.
如图,关于正方体\(ABCD-{{A}_{1}}{{B}_{1}}{{C}_{1}}{{D}_{1}}\),下面结论错误的是\((\) \()\)
如图,在直四棱柱\(ABCD-A_{1}B_{1}C_{1}D_{1}\)中,\(DB=BC\),\(DB⊥AC\),点\(M\)是棱\(BB_{1}\)上一点.
\((1)\)求证:\(B_{1}D_{1}/\!/\)平面\(A_{1}BD;\)
\((2)\)求证:\(MD⊥AC;\)
如图,长方体\(ABCD—A_{1}B_{1}C_{1}D_{1}\)中,试在\(DD_{1}\)确定一点\(P\),使得直线\(BD_{1}/\!/\)平面\(PAC\),并证明你的结论.
如图,直三棱柱\(ABC-{{A}_{1}}{{B}_{1}}{{C}_{1}}\)中,\(D\),\(E\)分别是\(AB\),\(B{{B}_{1}}\)的中点,\(A{{A}_{1}}=AC=CB=\dfrac{\sqrt{2}}{2}AB\).
\((1)\)证明:\(B{{C}_{1}}/\!/\)平面\({{A}_{1}}CD\);
\((2)\)求异面直线\(B{{C}_{1}}\)和\({{A}_{1}}D\)所成角的大小;
在如图所示的几何体中,四边形\({ABCD}\)是等腰梯形,\({AB}{/\!/}{CD}\),\({∠}DAB{=}60^{{∘}}\),\({FC}{⊥}{平面}{\ ABCD}\),\({AE}{⊥}{BD}\),\(CB{=}CD{=}CF\).
\((1)\)求证:\({BD}{⊥}{平面}{\ AED}\);
\((2)\)求二面角\(F{-}{BD}{-}C\)的余弦值.
已知直线\(l\not\subset \)平面\(\alpha \),直线\(m\subset \)平面\(\alpha \),下面四个结论:\(①\)若\(l\bot \alpha \),则\(l\bot m\);\(②\)若\(l\parallel \alpha \),则\(l\parallel m\);\(③\)若\(l\bot m\)则\(l\bot \alpha \);\(④\)若\(l\parallel m\),则\(l\parallel \alpha \),其中正确的是( )
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如图,在四棱锥\(P-ABCD\)中,底面\(ABCD\)是矩形,点\(E\)在棱\(PC\)上\((\)异于点\(P\),\(C)\),平面\(ABE\)与棱\(PD\)交于点\(F\).
\((1)\)求证:\(AB\parallel EF\);
\((2)\)若平面\(PAD\bot \)平面\(ABCD\),求证:\(AF\bot EF\).
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