共50条信息
在正方形\(ABCD{-}A_{1}B_{1}C_{1}D_{1}\)中,\(E\)为棱\({CD}\)的中点,则( )
如图,正方体\(ABCD-A_{1}B_{1}C_{1}D_{1}\)的棱长为\(1\),\(P\),\(Q\)分别是线段\(AD_{1}\)和\(B_{1}C\)上的动点,且满足\(AP=B_{1}Q\),则下列命题错误的是\((\) \()\)
已知\(\triangle ABC\)是等腰直角三角形,\(∠BAC=90^{\circ}\),\(AD⊥BC\),\(D\)为垂足,以\(AD\)为折痕,将\(\triangle ABD\)和\(\triangle ACD\)折成互相垂直的两个平面后,如图所示,有下列结论:
\(①BD⊥CD\);\(②BD⊥AC\);
\(③AD⊥\)面\(BCD\);\(④\triangle ABC\)是等边三角形.
其中正确的结论的个数为\((\) \()\)
正三棱柱\(ABC-{{A}_{1}}{{B}_{1}}{{C}_{1}}\)中,若\(AB=\sqrt{2}B{{B}_{1}}\),则\(A{B}_{1} \)与\({C}_{1}B \)所成角的大小为\((\) \()\)
如图长方体中,\(AB=AD=2\sqrt{3}\),\(CC_{1}=\sqrt{2}\),则二面角\(C_{1}—BD—C\)的大小为\((\) \()\)
如图,\({ABCD}{-}A_{1}B_{1}C_{1}D_{1}\)为正方体,下面结论错误的是\(({ })\)
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