共50条信息
如图,在四棱锥\(P-ABCD\)中,\(AB/\!/CD\),且\(∠BAP=∠CDP={90}^{^{\circ}} \)
\((1)\)证明:平面\(PAB⊥\)平面\(PAD\);
\((2)\)若\(PA=PD=AB=DC\),\(∠APD={90}^{^{\circ}} \),求二面角\(A-PB-C\)的余弦值.
如图,四棱锥\(P-ABCD\)的底面\(ABCD\)是矩形,平面\(PAB\bot \)平面\(ABCD\),\(E\)是\(PA\)的中点,且\(PA=PB=AB=2\),\(BC=\sqrt{2}\).
\((1)\)求证:\(PC/\!/\)平面\(EBD\);
\((2)\)求三棱锥\(A-PBD\)的体积.
若\(l\) 、\(m\)、\(n\)是互不相同的空间直线,\(α\)、\(β\)是不重合的平面,下列命题中为真命题的是\((\) \()\)
对于四面体\(ABCD\),给出下列四个命题:
\(①\)若\(AB=AC\),\(BD=CD\),则\(BC⊥AD\);\(②\)若\(AB=CD\),\(AC=BD\),则\(BC⊥AD\);
\(③\)若\(AB⊥AC\),\(BD⊥CD\),则\(BC⊥AD\);\(④\)若\(AB⊥CD\),\(AC⊥BD\),则\(BC⊥AD\).
其中为真命题的是\((\) \()\)
如图,正方体\(ABCD-{{A}_{1}}{{B}_{1}}{{C}_{1}}{{D}_{1}}\)中,有以下结论:\(①BD/\!/\)平面\(C{{B}_{1}}{{D}_{1}}\); \(②A{{C}_{1}}\bot BD\); \(③A{{C}_{1}}\bot \)平面\(C{{B}_{1}}{{D}_{1}}\);\(④\)直线\({{B}_{1}}{{D}_{1}}\)与\(BC\)所成的角为\(45{}^\circ .\)其中正确的结论个数是
如图,三棱柱\(ABC-A_{1}B_{1} C_{1}\)中,\(AA_{1}C_{1} C\)是边长为\(4\)的正方形\(.\)平面\(ABC⊥\)平面\(AA_{1}C_{1} C\),\(AB=3\),\(BC=5\),
\((1)\)求证:\(AA_{1}⊥\)平面\(ABC\);
\((2)\)求二面角\(A_{1}-BC_{1}-B_{1}\)的余弦值;
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