Question

find angle between vectors a vector equal to i cap +4j cap - 2k cap and b vector equal to 2i cap - 3j cap + 4k cap.
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Answer 1

$\cos( \alpha ) = \frac{a.b}{ |a| |b| }$

$a.b = 2 - 12 - 8 = - 18$

$|a| |b| = \sqrt{21} \times \sqrt{29} = \sqrt{609}$

$\alpha = \ { \cos }^{ - 1} \frac{ - 18}{ \sqrt{609} }$