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Let a and b be two unit vectors. If the vectors c = a +2 b and d =5 a -4 b are perpendicular to each other, then the angle between a and b is

Options

  1. A6
  2. B2
  3. C3
  4. D4

Correct answer

C. 3

Step-by-step solution

c d = 0 5| a |^2+6 a b -8| b |^2=0 6 a b =3 a b = 1 2 ( a b )= 3

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