共50条信息
如图所示,已知四边形\(ABCD\)是正方形,四边形\(ACEF\)是矩形,\(AB=2\),\(AF=1\),\(M\)是线段\(EF\)的中点.
\((1)\)求证:\(MA/\!/\)平面\(BDE\).
\((2)\)若平面\(ADM∩\)平面\(BDE=l\),平面\(ABM∩\)平面\(BDE=m\),试分析\(l\)与\(m\)的位置关系,并证明你的结论.
\(AD/\!/BC\),\(AB=BC= \dfrac{1}{2}AD\),\(E\),\(F\),\(H\)分别为线段\(AD\),\(PC\),\(CD\)的中点,\(AC\)与\(BE\)交于\(O\)点,\(G\)是线段\(OF\)上一点.
\((1)\)求证:\(AP/\!/\)平面\(BEF\);
\((2)\)求证:\(GH/\!/\)平面\(PAD\).
如图,在\(\triangle ABC\)中,\(∠B=90^{\circ}\),\(AB=\sqrt{2}\),\(BC=1\),\(D\),\(E\)两点分别是边\(AB\),\(AC\)的中点,现将\(\triangle ABC\)沿\(DE\)折成直二面角\(A-DE-B\).
\((2)\)求直线\(AD\)与平面\(ABE\)所成角的正切值.
如左图,四边形\(ABCD\)中,\(AB/\!/CD\),\(AD⊥AB\),\(AB=2CD=4\),\(AD=2\),过点\(C\)作\(CO⊥AB\),垂足为\(O\),将\(\triangle OBC\)沿\(CO\)折起。如右图,使得平面\(CBO\)与平面\(AOCD\)所成的二面角的大小为\((θ < θ < π)\),\(E\)、\(F\)分别为\(BC\)、\(AO\)的中点.
\((1)\)求证:\(EF/\!/\)平面\(ABD\);
\((2)\)若\(\theta =\dfrac{\pi }{3}\),求二面角\(F—BD—O\)的余弦值.
在边长为\(4\)的菱形\(ABCD\)中,\(\angle DAB=60{}^\circ \),点\(E,F \)分别是边\(CD,CB \)的中点,\(AC\bigcap EF=O\),沿\(EF\)将\(∆CEF \)翻折到\(∆PEF \),连接\(PA,PB,PD \),得到如图所示的五棱锥\(P-ABFED\),且\(PB=\sqrt{10}\).
\((1)\)求证:\(BD\bot PA\);
\((2)\)求四棱锥\(P-BFED\)的体积.
如图所示,平面四边形\(ABCD\)的四个顶点\(A\),\(B\),\(C\),\(D\)均在平行四边形\(A′B′C′D′\)所确定的平面\(α\)外,且\(AA′\),\(BB′\),\(CC′\),\(DD′\)互相平行.
\((1)\)求证:平面\(AA′D′D/\!/\)平面\(BB′C′C\) ;
\((2)\)求证:四边形\(ABCD\)是平行四边形.
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