共50条信息
如图,在\(\triangle ABC\)中,\(AB=2\),\(BC=3\),\(∠ABC=60^{\circ}\),\(AH⊥BC\)于点\(H\),\(M\)为\(AH\)的中点\(.\)若\(\overrightarrow{AM} =λ\overrightarrow{AB} +μ\overrightarrow{BC} \),则\(λ+μ=\)________.
已知\(\overrightarrow{a}=\left(2,-1,3\right), \overrightarrow{b}=\left(-1,4,-2\right), \overrightarrow{c}=\left(7,5,λ\right) \)若\(\overrightarrow{a}, \overrightarrow{b}, \overrightarrow{c} \)三向量不能构成空间的一个基底,则实数\(\lambda \)的值为\((\) \()\)。
已知边长都为\(1\)的正方形\(ABCD\)与\(DCFE\)所在的平面互相垂直,点\(P\)、\(Q\)分别是线段\(BC\)、\(DE\)上的动点\((\)包括端点\()\),\(PQ= \sqrt{2} .\)设线段\(PQ\)中点的轨迹为\(Â\),则\(Â\) 的长度为\((\) \()\)
\((1)\)判断\(\overrightarrow{MA}\),\(\overrightarrow{MB}\),\(\overrightarrow{MC}\)三个向量是否共面;
\((2)\)判断点\(M\)是否在平面\(ABC\)内.
如图,在四棱锥\(S—ABCD\)中,底面梯形\(ABCD\)中,\(BC/\!/AD\),平面\(SAB⊥\)平面\(ABCD\),\(\triangle SAB\)是等边三角形,已知\(AC=2AB=4\),\(BC=2AD=2DC=2 \sqrt{5} \).
\((\)Ⅰ\()\)求证:平面\(SAB⊥\)平面\(SAC\);
\((\)Ⅱ\()\)求二面角\(B—SC—A\)的余弦值.
已知\(a\)、\(b\)是异面直线,\(A\)、\(B∈a\),\(C\)、\(D∈b\)的大小,\(AC⊥b\),\(BD⊥b\),且\(AB=2\),\(CD=1\),则\(a\)与\(b\)所成的角是________.
如图,平行六面体\(ABCD-{{A}_{1}}{{B}_{1}}{{C}_{1}}{{D}_{1}}\)中,\({{A}_{1}}{{C}_{1}}\)与\({{B}_{1}}{{D}_{1}}\)的交点为点\(M.\)设\(\overrightarrow{AB}=\overrightarrow{a}\),\(\overrightarrow{AD}=\overrightarrow{b}\),\(\overrightarrow{A{{A}_{1}}}=\overrightarrow{c}\),则\(\overrightarrow{AM}=\)__________;\((\)用向量\( \overrightarrow{a}, \overrightarrow{b}, \overrightarrow{c} \)表示\()\)
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