Let →a=^i−^j,→b=^j−^k,→c=^k−^i. If →d is a unit vector such that →a⋅→d=0=[→b→c→d], then →d is equal to:
A
±(^i+^j−2^k√6)
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B
±(^i+^j−^k√3)
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C
±(^i+^j+^k√3)
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D
±^k
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Solution
The correct option is A±(^i+^j−2^k√6) →d is perpendicular to →a and coplanar with →b and →c.
Hence, →d is a vector collinear with →a×(→b×→c) ⇒→d=±→a×(→b×→c)|→a×(→b×→c)|
Now →a×(→b×→c)=(→a⋅→c)→b−(→a⋅→b)→c =−1(^j−^k)+1(^k−^i) =−^i−^j+2^k
Hence, →d=±(^i+^j−2^k√6)