Let three vectors a → , b → and c → be such that c → is coplanar with a → and…

Let three vectors a,b and c be such that c is coplanar with a and b,a·c=7 and b is perpendicular to c, where a=-i^+j^+k^ and b=2i^+k^, then the value of 2a+b+c2 is

Solution

Let c=λb×a×b

=λb·ba-b·ab

=λ5-i^+j^+k^+2i^+k^

=λ-3i^+5j^+6k^

c·a=73λ+5λ+6λ=7

λ=12

 2-32-1+2i^+52+1j^+3+1+1k^2

=214+494+25=25+50=75

Asked in: JEE Main 2021 (24 Feb Shift 1)

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