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MHT CET202124 Sep 2021Evening ShiftMathematicsVector AlgebraActual

If the angle between the vectors a =2 ^2 i +4 j + k and b =7 i -2 j + k is obtuse, then

Options

  1. A(0, 1 2 ]
  2. B(0, 1 2 )
  3. C[0, 1 2 ]
  4. D[0, 1 2 )

Correct answer

B. (0, 1 2 )

Step-by-step solution

We have a =2 ^2 i +4 j + k and b =7 i -2 j + k a b =| a | | b | , where is angle between a and b . = a b | a | | b | < 0 , as is an obtuse angle. | a | | b | < 0 (2 ^2 )(7)+(4 )(-2)+(1)( ) < 0 14 ^2-7 < 0 7 (2 -1) < 0 (2 -1) < 0 0 < < 1 2 i.e. (0, 1 2 )

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