The vectors $\overrightarrow{AB} = 3 \hat{i} + 4 \hat{k}$ and $\overrightarrow{AC} = 5 \hat{i} - 2 \hat{j} + 4 \hat{k}$ are the sides of a triangle $ABC$. The length of the median through $A$ is

If $C$ is the mid-point of the line segment $AB$ and $P$ is any point outside the line $AB$,then

If $\vec{PO} + \vec{OQ} = \vec{QO} + \vec{OR}$,then

Let $\vec{i}+\vec{j}+\vec{k}$,$a_1 \vec{i}+b_1 \vec{j}+c_1 \vec{k}$,$a_2 \vec{i}+b_2 \vec{j}+c_2 \vec{k}$,and $a_3 \vec{i}+b_3 \vec{j}+c_3 \vec{k}$ be the position vectors of the points $A, B, C, D$ respectively. The position vector of the centroid of the triangular face $BCD$ is $\frac{2}{3}(\vec{i}+\vec{j}+\vec{k})$. If $\alpha \vec{i}+\beta \vec{j}+\gamma \vec{k}$ is the position vector of the centroid of the tetrahedron $ABCD$,then find the value of $2 \alpha+\beta+\gamma$.

If $P$ and $Q$ are the midpoints of the sides $BC$ and $CD$ of the parallelogram $ABCD$,then $\overrightarrow{AP} + \overrightarrow{AQ} = $

If the length of a vector is $21$ and its direction ratios are $2, -3, 6$,then its direction cosines are: