Q41 / 100 · NTA Abhyas (JEE Main) 2020 · Mathematics · Vector Algebra

Let a→, b→, c→ be three vectors of magnitude 3, 4, 5 respectively, satisfying a→b→c→=60. If a→+2b→+3c→·a→×c→×b→+b→=λ, then λ is equal to

  • A
    16
  • Correct answer
    B
    32
  • C
    20
  • D
    40

Solution

Given, a→b→c→=3·4·5=60
Also, a→b→c→=60⇒a→b→c→=a→b→c→
⇒a→,b→,c→ are mutually perpendicular vectors
Also, a→×c→×b→+b→=a→·b→c→-c→·b→a→+b→
=b→
Hence, a→+2b→+3c→·b→=2b→2=32

Hence, the correct answer is option: 'B'.

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