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If a unit vector a makes angles π /3 with i ˆ , π /4 with j ˆ and θ ∈ (0, π ) with k ˆ , then a value of θ is :

1. 12 5 π
2. 6 5 π
3. 4 π
4. 3 2 π

Correct answer: 3 2 π

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