The angle between two vectors - 2î + 3ĵ +

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The angle between two vectors $ - 2\hat i + 3\hat j + \hat k$ and $\hat i + 2\hat j - 4\hat k$ is ....... $^o$

A

$0$

B

$90$

C

$180$

D

None of the above

The angle between two vectors $ - 2\hat i + 3\hat j + \hat k$ and $\hat i + 2\hat j - 4\hat k$ is ....... $^o$

$\cos \theta = \frac{{\vec A.\vec B}}{{|\vec A||\vec B|}} = \frac{{ - 2 + 6 - 4}}{{\sqrt {14} \sqrt {21} }} = 0$ 

$\therefore \theta = 90^\circ $