Let α   ∈ R and the three vectors a → = α i ^ + j ^ + 3 k ^ ,    b…

Let αR and the three vectors a=αi^+j^+3k^,  b=2i^+j^-αk^ and c=αi^-2j^+3k^. Then the set S = {α:a,b and c are coplanar}
  1. is singleton
  2. contains exactly two positive numbers
  3. is empty
  4. contains exactly two numbers only one of which is positive

Solution

If a, b and c are coplanar then, 
α1321-αα-23=0
3α2+18=0
αϕ

Asked in: JEE Main 2019 (12 Apr Shift 2)

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