Let c → be a vector perpendicular to the vectors a → = i ^ + j ^ - k ^ and b → = i ^ + 2 j…

Let c be a vector perpendicular to the vectors a=i^+j^-k^ and b=i^+2j^+k^. If c·(i^+j^+3k^)=8, then the value of c·(a×b) is equal to

Solution

c=λ(a×b)

a×b=i^j^k^11-1121

(a×b)=3i^-2j^+k^

c·(i^+j^+3k^)=λ(3i^-2j^+k^)·(i^+j^+3k^)

λ(4)=8λ=2

c=2(a×b)

Hence, c·(a×b)=28

Asked in: JEE Main 2021 (16 Mar Shift 2)

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