共50条信息
如图,\(AB/\!/\)平面\(\alpha /\!/\)平面\(\beta \),过\(A\),\(B\)的直线\(m\),\(n\)分别交\(\alpha \)、\(\beta \)于\(C\),\(E\)和\(D\),\(F\),若\(AC=2\),\(CE=3\),\(BF=4\),则\(BD\)的长为____________.
如图,在四棱锥\(P-ABCD\)中,\(PA⊥\)底面\(ABCD\),底面\(ABCD\)为梯形,\(AD/\!/BC\),\(CD=\)\(\sqrt{5}\) ,\(PA=AD=AB=2BC=2\),过\(AD\)的平面分别交\(PB\),\(PC\)于\(M\),\(N\)两点.
\((\)Ⅱ\()\)若\(M\)为\(PB\)的中点,求二面角\(P-DN-A\)的余弦值.
如图,在三棱柱\(ABC-{A}_{1}{B}_{1}{C}_{1} \)中,\(AB⊥ \)平面\(A{A}_{1}{C}_{1}C \),\(A{A}_{1}=AC .\)过\(A{A}_{1} \)的平面交\({B}_{1}{C}_{1} \)于点\(E\),交\(BC\)于点\(.F\)
\((\)Ⅰ\()\)求证:\({A}_{1}C⊥ \)平面\(AB{C}_{1} \);
\((\)Ⅱ\()\)记四棱锥\({B}_{1}-A{A}_{1}EF \)的体积为\({V}_{1} \),三棱柱\(ABC-{A}_{1}{B}_{1}{C}_{1} \)的体积为\(V.\)若\(BF=FC\),证明\({{B}_{1}}E=E{{C}_{1}}\),并求\(\dfrac{{{V}_{1}}}{V}\)的值
已知\(E,F,G,H\)分别是空间四边形\(ABCD\)的边\(AB,BC,CD,DA\)上的点,且四边形\(EFGH\)是平行四边形,求证:\(EF/\!/AC\).
如图,四棱锥\(P-ABCD\)的底面边长为\(8\)的正方形,四条侧棱长均为\(2\sqrt{17}\)\(.\)点\(G,E,F,H\)分别是棱\(PB,AB,CD,PC\)上共面的四点,平面\(GEFH\bot \)平面\(ABCD\),\(BC/\!/\)平面\(GEFH\).
\((1)\)证明:\(GH/\!/EF;\)
\((2)\)若\(EB=2\),求四边形\(GEFH\)的面积.
进入组卷