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.
已知\(PA⊥⊙O\)所在的平面,\(AB\)是\(⊙O\)的直径,\(C\)是\(⊙O\)上任意一点,过\(A\)作\(AE⊥PC\)于\(E.\)求证:
\((1)AE⊥\)平面\(PBC;\)
\((2)\)平面\(PAC⊥\)平面\(PBC\).
如图,在三棱锥\(A-BCD\)中,\(BD{=}CD\),\(E\)为\(AC\)的中点\(. O\)为\(BC\)上一点,\(AO\bot \)平面\(BCD\),\(DO\bot BC\).
求证:\((1)AB/\!/\)平面\(ODE\);
\((2)\)平面\(ABC⊥\)平面\(ODE\).
如图,四边形\(ABCD\)为菱形,\(∠DAB=60^{\circ}\),\(M\)为\(BC\)中点,\(ED⊥\)平面\(ABCD\),\(ED=AD=2EF=2\),\(EF/\!/AB\).
\((\)Ⅰ\()\)求证:\(FM/\!/\)平面\(BDE\);
\((\)Ⅱ\()\)若\(G\)为线段\(BE\)上的点,当三棱锥\(G—BCD\)的体积为\(\dfrac{2\sqrt{3}}{9}\)时,求面\(\dfrac{BG}{BE}\)的值.
如图所示,四面体\(ABCD\)中,\(E\),\(F\)分别为\(AC\),\(AD\)的中点,则直线\(CD\)与平面\(BEF\)的位置关系是( )
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,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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