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AP EAMCET2011MathematicsVector Algebra

If | a |=1,| b |=2 and the angle between a and b is 120^ , then ( a +3 b ) (3 a - b ) ^2 is equal to

Options

  1. A425
  2. B375
  3. C325
  4. D300

Correct answer

D. 300

Step-by-step solution

aligned & ( a +3 b ) (3 a - b ) ^2 & = 3 a a - a b +9 b a -3 b b ^2 & = -10 a b ^2 & =100 [| a || b | n 120^ ]^2 & =100 [1 2 n 3 2 ]^2=100 3=300 aligned

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