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MHT CET202120 Sep 2021Evening ShiftMathematicsVector AlgebraActual

a , b and c are three vectors such that a + b + c = 0 and | a |=3,| b |=5,| c |=7 , then the angle between a and b is

Options

  1. A4
  2. B2
  3. C3
  4. D6

Correct answer

C. 3

Step-by-step solution

a + b + c =0 c =-( a + b ) and let angle between a and b be aligned & | c |^2=( a + b )^2=| a |^2+| b |^2+2 a b & =| a |^2+| b |^2+2| a | | b | & (7)^2=(3)^2+(5)^2+2(3)(5) & 49=9+25+30 = 15 30 = 1 2 = 3 aligned

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