What are coordinates?

• When we want to plot a point on a graph we need to know where to put it
• If the horizontal axis is labelled?x?and the vertical axis is labelled?y, then the?x?and?y?coordinates?are how far we go along the?x?and?y?axes to plot the point

What can we do with coordinates?

• If we have two points with coordinates (x₁, y₁) and (x₂, y₂) then we should be able to find
  • the?gradient?of the line through them
  • the?midpoint?of the two points
  • the?distance?between the two points

   

• Don’t get fazed by the horrid notation (x₁, y₁) – this is just “point 1” and the other is “point 2” so we put the little numbers (subscripts) in so that we know which coordinate we are referring to. In questions there’ll be lots of nice numbersHere’s how we do each of those:

• You should also know that three points A, B and C lie on the same STRAIGHT LINE if AB and AC (or BC) have the same gradient