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COMEDK2017MathematicsVector Algebra

If a = i + j +2 k and b =3 i +2 j - k , then find (a+3 b) (2 a-b) .

Options

  1. A-15
  2. B12
  3. C13
  4. D-10

Correct answer

A. -15

Step-by-step solution

Here, a +3 b = i + j +2 k +3(3 i +2 j - k )=10 i +7 j - k and 2 a - b =2( i + j +2 k )-(3 i +2 j - k )=- i +5 k ( a +3 b ) (2 a - b )=(10 i +7 j - k ) (- i +5 k )=10 (-1)+7 0+-1 5=-15

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