Let a,b and c be three non-coplanar vectors and let p,q and r be vectors defined by the relations p=b×cabc,q=c×aabc and r=a×babc Then the value of the expression (a+b).p+(b+c).q+(c+a).r is equal to
A
0
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B
1
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C
2
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D
3
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Solution
The correct option is C3 Given that, p=b×cabc,q=c×aabc and r=a×babc ∴a.p=a.(b×c)abc=a.(b×c)abc=1 And a.q=a.(c×a)abc=a.(c×a)abc=0 similarly, b.q=c.r=1 And a.r=bq=cq=c.p=br=0 ∴a+b.p+b+c.q+c+q.r =a.p+b.p+bq+c.q+c.r+a.r =1+1+1=3