If →a,→b and →c are any three non-zero vectors in space, then the value of (→c+→b)×(→c+→a)⋅(→c+→b+→a) is :
A
[→a→b→c]
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B
2[→a→b→c]
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C
0
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D
3[→a→b→c]
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Solution
The correct option is A[→a→b→c] Let E=(→c+→b)×(→c+→a)⋅(→c+→b+→a) ⇒E=(→c×→c+→c×→a+→b×→c+→b×→a)⋅(→c+→b+→a)
Since →c×→c=→0, ⇒E=(→c×→a+→b×→c+→b×→a)⋅(→c+→b+→a)
On multiplying (taking dot product) term by term, we have ⇒E=→b×→a⋅→c+→c×→a⋅→b+→b×→c⋅→a ⇒E=−[→a→b→c]+[→a→b→c]+[→a→b→c] ⇒E=[→a→b→c]