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NDA2015MathematicsThree Dimensional GeometryActual

The direction ratios of the line perpendicular to the lines with direction ratios 1,-2,-2 and 0,2,1 are

Options

  1. A2,-1,2
  2. B-2,1,2
  3. C2,1,-2
  4. D-2,-1,-2

Correct answer

A. 2,-1,2

Step-by-step solution

Let the direction ratio be a , b , c aligned & 90^ = (a)(1)+(b)(-2)+(c)(-2) a ^2+ b ^2+ c ^2 (1)^2+(-2)^2+(-2)^2 & a -2 ~b -2 c =0....(1) & 90^ = ( a )(0)+ b (2)+( c )(1) a ^2+ b ^2+ c ^2 (0)^2+(-2)^2+(1)^2 & 2 ~b + c =0....(2) aligned From eq. (1) & (2) a =-2 ~b ; c =-2 ~b

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