Straight Line

• What is the general equation of a straight line?

  ax + by + c = 0
• Parallel lines have equal gradients.
• Perpendicular lines have product of their gradients equal to -1.
• A set of points which lie on the same straight line are said to be collinear.
• If the lines share a common point and have the same gradient then they are collinear.
• The altitude of a triangle is a line drawn from one vertex which meets the opposite side at right angles (perpendicular)