If | A |=2,| B |=5 and | A × B |=8 Angle between A and B is acute, then A · B is

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3-1.Vectors

easy

If $| A |=2,| B |=5$ and $| A \times B |=8$ Angle between $A$ and $B$ is acute, then $A \cdot B$ is

A$6$

B$3$

C$4$

D$7$

Solution

(a)
$8=(5)(2) \sin \theta$
$\therefore \sin \theta=4 / 5$
$\text { or } \cos \theta=3 / 5$
$\therefore A \cdot B =A B \cos \theta=(5)(2)(3 / 5)=6$

Standard 11

Physics

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