Q 11-03-019NEETJEE MainEasy
The angle between the vectors $\vec{A} = 2\hat{i} + 2\hat{j} - \hat{k}$ and $\vec{B} = 6\hat{i} - 3\hat{j} + 2\hat{k}$ is
Answer: (D) $\cos^{-1}\left(\dfrac{4}{21}\right)$
$$\vec{A}\cdot\vec{B} = 12 - 6 - 2 = 4, \qquad |\vec{A}| = 3, \qquad |\vec{B}| = 7$$
$$\cos\theta = \frac{4}{3 \times 7} = \frac{4}{21}$$
Solution by Sreeraj P, M.Sc Physics