Q31 / 100 · NTA Abhyas (JEE Main) 2020 · Mathematics · Vector Algebra

Let a→, b→ and c→ be three vectors such that a→=2, b→=1 and c→=3. If the projection of b→ along a→ is double of the projection of c→ along a→ and b→, c→ are perpendicular to each other, then the value of a→-b→+2c→22 is equal to

  • A
    41
  • B
    14
  • C
    14
  • Correct answer
    D
    20.5

Solution

Given, b→⋅c→=0

 b→⋅a^=2c→⋅a^⇒b→⋅a→=2c→⋅a→

So, a→-b→+2c→2=a→2+b→2+4c→2-2a→⋅b→-4b→⋅c→+4a→⋅c→

a→-b→+c→22=4+1+362=20.5

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

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