For any three vectors $a, b, c$,the condition $a \times (b \times c) = (a \times b) \times c$ holds if:

If $\overline{b}$ and $\overline{c}$ are unit vectors and $|\bar{a}|=7$,$\bar{a} \times(\bar{b} \times \bar{c})+\bar{b} \times(\bar{c} \times \bar{a})=\frac{1}{2} \bar{a}$,then the angle between the vectors $\bar{a}$ and $\overline{c}$ and the angle between the vectors $\overline{b}$ and $\overline{c}$ are respectively.

Let $\overline{a}, \overline{b}$ and $\overline{c}$ be three unit vectors such that $\overline{a} \times(\overline{b} \times \overline{c})=\frac{\sqrt{3}}{2}(\overline{b}+\overline{c})$. If $\overline{b}$ is not parallel to $\overline{c}$,then the angle between $\overline{a}$ and $\overline{b}$ is

Let $\vec{x}, \vec{y}$ and $\vec{z}$ be three vectors each of magnitude $\sqrt{2}$ and the angle between each pair of them is $\frac{\pi}{3}$. If $\vec{a}$ is a nonzero vector perpendicular to $\vec{x}$ and $\vec{y} \times \vec{z}$ and $\vec{b}$ is a nonzero vector perpendicular to $\vec{y}$ and $\vec{z} \times \vec{x}$,then
$(A)$ $\vec{b}=(\vec{b} \cdot \vec{z})(\vec{z}-\vec{x})$
$(B)$ $\vec{a}=(\vec{a} \cdot \vec{y})(\vec{y}-\vec{z})$
$(C)$ $\vec{a} \cdot \vec{b}=-(\vec{a} \cdot \vec{y})(\vec{b} \cdot \vec{z})$
$(D)$ $\vec{a}=(\vec{a} \cdot \vec{y})(\vec{z}-\vec{y})$

If $a=2 \hat{i}-3 \hat{j}+\hat{k}$, $b=\hat{i}-\hat{j}+2 \hat{k}$ and $c=2 \hat{i}+\hat{j}+\hat{k}$ are three vectors, then $|(a \times b) \times c|=$

If $\overline{a}=\frac{1}{\sqrt{10}}(3 \hat{i}+\hat{k})$ and $\overline{b}=\frac{1}{7}(2 \hat{i}+3 \hat{j}-6 \hat{k})$,then the value of $(\overline{a}-2 \overline{b}) \cdot \{(\overline{a} \times \overline{b}) \times (2 \overline{a}+\overline{b})\}$ is