Q32 / 100 · NTA Abhyas (JEE Main) 2020 · Mathematics · Vector Algebra

If  a→, b→ and c→ are three vectors, such that a→=2, b→=3, c→=4, a→⋅c→=0, a→⋅b→=0 and the angle between b→ and c→ is π3, then the value of a→×2b→-3c→ is equal to

  • Correct answer
    A
    123
  • B
    63
  • C
    33
  • D
    5

Solution

2b→-3c→2=4b→2+9c→2-12b→⋅c→
=36+144-12×3×4×12
=108
2b→-3c→=63
As we know that,
a→×2b→-3c→2+a→⋅2b→-3c→2=a→22b→-3c→2
⇒a→×2b→-3c→2+0=4×108
⇒a→×2b→-3c→=123

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

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