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AP EAMCET202021 Sep 2020Evening ShiftMathematicsThree Dimensional GeometryActual

If two lines are parallel to each other, then which of the following is true? (if ( (l₁, m₁, n₁ ) ) and ( (l₂, m₂, n₂ ) ) are direction cosines of the two lines).

Options

  1. A(I₁ I₂+m₁ m₂+n₁ n₂=0 )
  2. B( (l₁ l₂-m₂ m₁ )^2=0 )
  3. C( l₁ l₂ = m₁ m₂ = n₁ n₂ )
  4. D(l₁ l₂+m₁ m₂+n₁ n₂=1 )

Correct answer

C. ( l₁ l₂ = m₁ m₂ = n₁ n₂ )

Step-by-step solution

The two lines having direction ( cosines l₁, m₁, n₁ ) and (l₂, m₂, n₂ ) respectively are parallel to each other, then ( l₁ l₂ = m₁ m₂ = n₁ n₂ ) Hence, option (c) is correct.

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