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AP EAMCET202018 Sep 2020Morning ShiftMathematicsThree Dimensional GeometryActual

Which of the following is false? 1. If ((a, b, c) ) are direction ratios of a line, then (a^2+b^2+c^2 1 ). 2. The direction cosines of a line can be its direction ratios but not vice-versa. 3. If ((l, m, n) ) is one set of direction cosines, then ((-l,-m,-n) ) is also a valid set. 4. If ( (l₁, m₁, n₁ ) ) and ( (l₂, m₂, n₂ ) ) are direction cosines of perpendicular lines, then (l₁ l₂+m₁ m₂+n₁ n₂=1 ).

Options

  1. A1
  2. B2
  3. C3
  4. D4

Correct answer

D. 4

Step-by-step solution

If the direction cosines of two perpendicular lines are (l₁, m₁, n₁ ) and (l₂, m₂, n₂ ), then (l₁ l₂+m₁ m₂+n₁ n₂=0 )

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