If →a,→b,→care three vectors such that |→a|=3, |→b|=1 and |→c|=2 and |→b×→c|=√3 and →b−3→c=λ→a, then the possible value of [λ] is (where [.] denotes greatest integer function)
A
1
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B
2
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C
3
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D
5
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Solution
The correct option is C3 |→b×→c|=|→b||→c|sinθ |→b||→c|sinθ=√3 1×2×sinθ=√3 sinθ=√32−(1)
Now →b−3→c=λ→a
Squaring both sides (→b−3→c)2=(λ→a)2 |→b|2−6(→b⋅→c)+9|→c|2=λ2|→a|2 |→b|2−6|→b||→c|cosθ+9|→c|2=λ2|→a|2 12−6×1×2×12+9(2)2=9λ2 λ=±319 [λ]=3 or [λ]=−4