JEE Main 2018MathematicsVector AlgebraEasyMCQ

JEE Main 2018 — Vector Algebra Question with Solution

JEE Main 2018 (08 Apr)

Question

Let u→ be a vector coplanar with the vectors a→=2i^+3j^-k^ and b→= j^+k^ . If u→ is perpendicular to a→ and u→⋅b→=24, then u→2 is equal to:

Choose an option

Show full solutionCorrect option: B
Correct answer
B336

Step-by-step explanation

As  u → =λ[ a → ×( a → × b → ) ]

u → =λ[ [ a → . b → ] a → −| a → | 2 b → ]

u → =λ[ 2 a → −14 b → ]

u → . b → =2λ[ a → .  b → −7| b → | 2 ]

=2λ[ 2−14 ]

24=−24λ

λ=−1

u → =14 b → −2 a →

u→=-4i^+8j^+16k^

| u → | 2 = 4 2 + 8 2 + 16 2

=336

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About this question

This is a previous-year question from JEE Main 2018, 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.