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Let → a = i ˆ – j ˆ , → b = i ˆ + j ˆ + k ˆ and → c be a vector such that → a × → c + → b = → 0 and → a . → c = 4, then 2 | c | → is equal to :

1. 2 19
2. 8
3. 2 17
4. 9

Correct answer: 2 19

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