JEE Main 2021MathematicsVector AlgebraEasyNumerical

JEE Main 2021 — Vector Algebra Question with Solution

JEE Main 2021 (16 Mar Shift 2)

Question

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

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Show full solutionCorrect answer: 28
Correct answer
28

Step-by-step explanation

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)=8⇒λ=2

c→=2(a→×b→)

Hence, c→·(a→×b→)=28

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About this question

This is a previous-year question from JEE Main 2021, covering the Vector Algebra chapter of Mathematics. PrepSharp catalogues every PYQ from JEE Main with a verified answer key and step-by-step solution prepared by IIT alumni — so you can search by chapter, topic or year and revise efficiently.