共50条信息
设\(α\),\(β\),\(γ\)为两两不重合的平面,\(l\),\(m\),\(n\)为两两不重合的直线,给出下列三个说法:\(①\)若\(α⊥γ\),\(β⊥γ\),则\(α/\!/β\);\(②\)若\(α/\!/β\),\(l⊂α\),则\(l/\!/β\);\(③\)若\(α∩β=l\),\(β∩γ=m\),\(γ∩α=n\),\(l/\!/γ\),则\(m/\!/n.\)其中正确的说法个数是\((\) \()\)
已知\(l\),\(m\),\(n\)是三条直线,\(\alpha \)是一个平面,下列命题中正确命题的个数是( )
\(①\)若\(l\bot \alpha \),则\(l\)与\(\alpha \)相交; \(②\)若\(l\parallel \alpha \),则\(\alpha \)内有无数条直线与\(l\)平行;
\(③\)若\(m\subset \alpha \),\(n\subset \alpha \),\(l\bot m\),\(l\bot n\),则\(l\bot \alpha \);\(④\)若\(l\parallel m\),\(m\parallel n\),\(l\bot \alpha \)则\(n\bot \alpha \).
下列结论中,正确的有 ( )
\(①\)若\(a\not\subset \alpha \),则\(a/\!/α\);
\(②a/\!/\)平面\(α\),\(b⊂α\),则\(a/\!/b\);
\(③\)平面\(α/\!/\)平面\(β\),\(a⊂α\),\(b⊂β\),则\(a/\!/b\);
\(④\)平面\(α/\!/β\),点\(P∈α\),\(a/\!/β\),且\(P∈a\),则\(a⊂α\).
在直三棱柱\(ABC-A_{1}B_{1}C_{1}\)中,平面\(α\)与棱\(AB\),\(AC\),\(A_{1}C_{1}\),\(A_{1}B_{1}\)分别交于点\(E\),\(F\),\(G\),\(H\),且直线\(AA_{1}/\!/\)平面\(α.\)有下列三个命题:
\(①\)四边形\(EFGH\)是平行四边形;\(②\)平面\(α/\!/\)平面\(BCC_{1}B_{1}\);\(③\)平面\(α⊥\)平面\(BCFE\).
其中正确的命题有
已知直线\(a/\!/\)平面\(α\),\(a/\!/\)平面\(β\),\(α∩β=b\),则\(a\)与\(b \)( )
已知正方体\(ABCD-A_{1}B_{1}C_{1}D_{1}\)的棱长为\(2\),点\(P\)是\(AA_{1}D_{1}D\)的中心,点\(Q\)是上底而\(A_{1}B_{1}C_{1}D_{1}\)上一点,且\(PQ/\!/\)平面\(AA_{1}B_{1}B\),则线段\(PQ\)的长的最小值为\((\) \()\)
进入组卷