Properties of Lines


if two lines are parallel, their gradients are the same.

if two lines are perpendicular, the product of their gradients is -1.

if points are collinear, they lie on the same straight line.

Key Skills

  • given the equations of lines show whether they are parallel or perpendicular
  • find the equations of parallel or perpendicular lines given some information about them
  • show whether three or more points are collinear


parallelperpendicularproduct, collineargradientreciprocal.