Let the vectors 2 + a + b i ^ + a + 2 b + c j ^ - b + c k ^ ,   1 + b i ^ + 2 b j ^ - b k ^ and 2 + b i…

Let the vectors 2+a+bi^+a+2b+cj^-b+ck^, 1+bi^+2bj^-bk^ and 2+bi^+2bj^+1-bk^, a,b,cR be co-planar. Then which of the following is true?
  1. 2b=a+c
  2. 3c=a+b
  3. a=b+2c
  4. 2a=b+c

Solution

If the vectors are co-planar,

a+b+2a+2b+c-b-cb+12b-bb+22b1-b=0

Now R1R1-R2, R3R3-R2 

So a+1a+c-cb+12b-b101=0

(a+1)2b-(a+c)(2b+1)-c(-2b)=0

2ab+2b-2ab-a-2bc-c+2bc=0

2b-a-c=02b=a+c

Asked in: JEE Main 2021 (25 Jul Shift 1)

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