Four vectors →a,→b,→c and →x satisfy the relation (→a⋅→x)→b=→c+→x where →b⋅→a≠1. The value of →x in terms of →a,→b and →c is equal to
A
(→a⋅→c)→b−→c(→a⋅→b−1)(→a⋅→b−1)
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B
→c→a⋅→b−1
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C
2(→a⋅→c)→b+→c→a.→b−1
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D
2(→a⋅→c)→c+→c→a⋅→b−1
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Solution
The correct option is A(→a⋅→c)→b−→c(→a⋅→b−1)(→a⋅→b−1) (→a⋅→x)→b=→c+→x…(1)
Taking dot product with →a (→a⋅→x)(→b⋅→a)=(→c⋅→a)+(→a⋅→x) ⇒(→a⋅→x)(→b⋅→a−1)=→c⋅→a ⇒→a⋅→x=→c⋅→a→b⋅→a−1…(2)
From (1) and (2), ⎛⎝→c⋅→a→b⋅→a−1⎞⎠→b=→c+→x⇒→x=⎛⎝→c⋅→a→b⋅→a−1⎞⎠→b−→c=(→a⋅→c)→b−→c(→a⋅→b−1)(→a⋅→b−1)