共50条信息
如图,在直三棱柱\(ABC—A_{1}B_{1}C_{1}\)中,\(∠BAC=90^{\circ}\),\(AB=AC=2\),点\(M\),\(N\)分别为\(A_{1}C_{1}\),\(AB_{1}\)的中点.
\((1)\)证明:\(MN/\!/\)平面\(BB_{1}C_{1}C\);
\((2)\)若\(CM⊥MN\),求三棱锥\(M—NAC\)的体积.
如图,在正方体\(ABCD-A_{1}B_{1}C_{1}D_{1}\)中,\(O\)为底面\(ABCD\)的中心,\(P\)是\(DD_{1}\)的中点,设\(Q\)是\(CC_{1}\)上的点,问:当点\(Q\)在什么位置时,平面\(D_{1}BQ/\!/\)平面\(PAO\)?
如图所示,平面四边形\(ABCD\)的四个顶点\(A\),\(B\),\(C\),\(D\)均在平行四边形\(A′B′C′D′\)所确定的平面\(α\)外,且\(AA′\),\(BB′\),\(CC′\),\(DD′\)互相平行.
\((1)\)求证:平面\(AA′D′D/\!/\)平面\(BB′C′C\) ;
\((2)\)求证:四边形\(ABCD\)是平行四边形.
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