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AP EAMCET2009MathematicsThree Dimensional Geometry

If a =- i + j +2 k , b =2 i - j - k and c =-2 i + j +3 k , then the angle between 2 a - c and a + b is

Options

  1. A4
  2. B3
  3. C2
  4. D3 2

Correct answer

B. 3

Step-by-step solution

Now, aligned 2 a - c & =2(- i + j +2 k )-(-2 i + j +3 k ) & = j + k aligned and aligned a + b & =- i + j +2 k +2 i - j - k & = i + k aligned Let be the angle between 2 a - c and a + b . array ll & = ( j + k ) ( i + k ) 1^2+1^2 1^2+1^2 & = 1 2 2 = 1 2 array = 3

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