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If `vec a` and `vec b` are two unit vectors such that `vec a + 2 vec b` and `5 vec a - 4 vec b` are perpendicular to each other then the angle between `vec a` and `vec b` is

A

`45^(o)`

B

`60^(o)`

C

`cos^(-1)(1/3)`

D

`cos^(-1)(2/7)`

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The correct Answer is:
B
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