Relative positions of two lines

In space, two distinct lines can beoncurrent, parallel or reverse:

We have to consider two particular cases:

• perpendicular lines:

• orthogonal lines:
  
  
  

Euclid's Postulate or Parallel Lines

P₁₀) Given a straight line r and a point P r there is a single straight line s, drawn by P, such that r // s:

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