共50条信息
如图,在长方体\(ABCD-A\)\(1\)\(B\)\(1\)\(C\)\(1\)\(D\)\(1\)中,\(O\)为\(AC\)的中点,设\(E\)是棱\(DD_{1}\)上的点,且\(\overrightarrow{DE}= \dfrac{2}{3}\overrightarrow{DD_{1}}\),若\(\overrightarrow{EO}=x\overrightarrow{AB}+y\overrightarrow{AD}+z\overrightarrow{AA_{1}}\),试求\(x\),\(y\),\(z\)的值.
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\((\) \()\)。
\((1)\)证明:\(AC\)\(=\)\(AB\)\({\,\!}_{1}\);
\((2)\)若\(AC\)\(⊥\)\(AB\)\({\,\!}_{1}\),\(∠\)\(CBB\)\({\,\!}_{1}=60^{\circ}\),\(AB\)\(=\)\(BC\),求二面角\(A\)\(\)\(A\)\({\,\!}_{1}\)\(B\)\({\,\!}_{1}\)\(C\)\({\,\!}_{1}\)的余弦值.
已知\(S\)是\(\triangle ABC\)所在平面外一点,\(D\)是\(SC\)的中点,若\(\overrightarrow{BD}=x\overrightarrow{AB}+y\overrightarrow{AC}+z\overrightarrow{AS}\),则\(x+y+z=\)__________.
已知\(\overrightarrow{a}=(2,4,5)\),\(\overrightarrow{b}=(3,x,y)\)分别是直线\(l_{1}\)、\(l_{2}\)的方向向量\(.\)若\(l_{1}/\!/l_{2}\),则\((\) \()\)
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.
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