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

  • A
    $-3$
  • B
    $5$
  • C
    $3$
  • D
    $-5$

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$(D)$ $\mathbf{a} \cdot \mathbf{b}$$4. |\mathbf{a}||\mathbf{b}|$
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