共50条信息
已知三棱柱\(.ABC-A_{1}B_{1}C_{1}\)的侧棱与底面垂直,底面是边长为\(\sqrt{3}\)的正三角形\(.\)若\(P\)为底面\(A_{1}B_{1}C_{1}\)的中心,\(PA\)与平面\(ABC\)所成角的大小为\(\dfrac{\pi }{3}\),则棱柱\(ABC-A_{1}B_{1}C_{1}\)的体积为( )
如图,梯形\(ABCD\)中,\(AD= BC\),\(AB\parallel CD\),\(AC\bot BD\),平面\(BDFE\bot \)平面\(ABCD\),\(EF\parallel BD\),\(BE\bot BD\)
\((1)\)求证:平面\(AFC\bot \)平面\(BDFE;\)
\((2)\)若\(AB=2CD2\sqrt{2}\) ,\(BE = EF =2\),求\(BF\)与平面\(DFC\)所成角的正弦值.
如图,在\(Rt∆ABC \)中,\(AB=BC=3\),点\(E\)、\(F\)分别在线段\(AB\)、\(AC\)上,且\(EF/\!/BC \),将\(∆AEF \)沿\(EF\)折起到\(∆PEF \)的位置,使得二面角
\(P-EF-B \)的大小为\(60^{\circ} \).
\((1)\)求证:\(EF⊥PB \);
\((2)\)当点\(E\)为线段\(AB\)的靠近\(B\)点的三等分点时,求\(PC\)与平面\(PEF\)所成角\(\theta \)的正弦值.
正四棱锥\(P-ABCD\)的侧面是全等的正三角形,则侧棱\(PA\)与底面\(ABCD\)所成角的大小是________.
如图,三棱柱\(ABC-A_{1}B_{1}C_{1}\)中,各棱长均相等\(.D\),\(E\),\(F\)分别为棱\(AB\),\(BC\),\(A_{1}C_{1}\)的中点.
\((\)Ⅰ\()\)证明\(EF/\!/\)平面\(A_{1}CD\);
\((\)Ⅱ\()\)若三棱柱\(ABC-A_{1}B_{1}C_{1}\)为直棱柱,求直线\(BC\)与平面\(A_{1}CD\)所成角的正弦值.
如图,在四面体\(ABCD\)中,平面\(ACD⊥\)平面\(BCD\),\(\angle BCA=90{}^\circ \),\(AC=1\),\(AB=2\),\(\Delta BCD\)为等边三角形.
\((\)Ⅰ\()\)求证:\(AC⊥\)平面\(BCD\)
\((\)Ⅱ\()\)求直线\(CD\)与平面\(ABD\)所成角的正弦值.
已知边长为\(6\)的正方体\(ABCD-A_{1}B_{1}C_{1}D_{1}\),\(E\),\(F\)为\(AD\)、\(CD\)上靠近\(D\)的三等分点,\(H\)为\(BB_{1}\)上靠近\(B\)的三等分点,\(G\)是\(EF\)的中点.\((1)\)求\(A_{1}H\)与平面\(EFH\)所成角的正弦值;\((2)\)设点\(P\)在线段\(GH\)上,\( \dfrac {GP}{GH}=λ\),试确定\(λ\)的值,使得二面角\(P-C_{1}B_{1}-A_{1}\)的余弦值为\( \dfrac { \sqrt {10}}{10}\).
直三棱柱\((\)侧棱垂直于底面的三棱柱\()ABC—A_{1}B_{1}C_{1}\)中,底面是正三角形,三棱柱的高为\(\sqrt{3}\),若\(P\)是\(\triangle A_{1}B_{1}C_{1}\)的中心,且三棱柱的体积为\(\dfrac{9}{4}\),则\(PA\)与平面\(ABC\)所成角的大小是
正方体\(ABCD-A_{1}B_{1}C_{1}D_{1}\)中,\(BB_{1}\)与平面\(ACD_{1}\)所成角的余弦值为\((\) \()\)
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