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.
\((1)\)求证:\(PC/\!/\)平面\(BMN\);
\((2)\)求证:平面\(BMN⊥\)平面\(PAC\).
如图,在直四棱柱\(ABCD-A_{1}B_{1}C_{1}D_{1}\)中,已知\(DC=DD_{1}=2AD=2AB\),\(AD⊥DC\),\(AB/\!/DC\).
\((1)\)求证:\(D_{1}C⊥AC_{1}\);
\((2)\)问在棱\(CD\)上是否存在点\(E\),使\(D_{1}E/\!/\)平面\(A_{1}BD.\)若存在,确定点\(E\)位置;若不存在,说明理由.
如图,在三棱锥\(S-ABC\)中,\(SA⊥\)底面\(ABC\),\(AC=AB=SA=2\),\(AC⊥AB\),\(E\)是\(BC\)的中点,\(F\)在\(SE\)上,且\(SF=2FE.\)求证:\(AF⊥\)平面\(SBC\).
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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