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Let a,b and c be three non-coplanar vectors and r be any arbitrary vector. Then (a×b)×(r×c)+(b×c)×(r×a)+(c×a)×(r×b) i, always equal to

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a
[a→b→c→]r→
b
2[a→b→c→]r→
c
3[a→b→c→]r→
d
none of these

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detailed solution

Correct option is B

(a→×b→)×(r→×c→)=((a→×b→)⋅c→)r→−((a→×b→)⋅r→)⋅c→=[a→b→c→]r→−[a→b→r→]c→ Similarly, (b→×c→)×(r→×a→)=[b→c→a→]r→−[b→c→r→]a→ and (c→×a→)×(r→×b→)=[c→a→b→]r→−[c→a→r→]b→⇒ (a→×b→)×(r→×c→)+(b→×c→)×(r→×a→)+(c→×a→)×(r→×b→)=3[a→b→c→]r→−([b→c→r→]a→+[c→a→r→]b→+[a→b→r→]c→)=3[a→b→c→]r→−[a→b→c→]r→=2[a→b→c→]r→


Similar Questions

If a,b and c  are non-coplanar vectors a×c is perpendicular to a×(b×c)  then the value of [a×(b×c)]×c is equal to


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