Let→a=^i+^j+^k,→c=^j−^k and a vector →b be such that →a×→b=→c and →a.→b=3. Then |→b| equals :
A
113
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B
11√3
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C
√113
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D
√113
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Solution
The correct option is C√113 We have →a×→b=→c→a×(→a×→b)=→a×→c(→a.→b)→a−(→a.→a)→b=→a×→c3→a−3→b=−2^i+^j+^k3^i+3^j+3^k−3→b=−2^i+^j+^k→b=13(5^i+2^j+2^k)|→b|=√113