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Let a ˆ and b ˆ be two unit vectors such that the angle between them is 4 π . If θ is the angle between the vectors ( a ˆ + b ˆ ) and )) b ˆ a ˆ ( 2 b ˆ 2 a ˆ ( × + + , then the value of 164 cos 2 θ is equal to :

1. 90 + 2 27
2. 45 + 2 18
3. 90 + 2 3
4. 54 + 2 90

Correct answer: 90 + 2 27

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