Solve this following

Question:

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

  1. 5

  2. 3

  3. $-5$

  4. $-3$


Correct Option: , 3

Solution:

$=(2 \vec{a}-\vec{b}) \cdot(\vec{b}-2 \vec{a})$

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