On a set of axes (like the ones below), plot all the points which have an x coordinate of 3.
What do you notice about the position of all these points?

Now plot all the points which have a y coordinate of 5.
What do you notice about the position of these points?

Give the coordinates at the point where the two lines you have drawn meet.
We call this the point of intersection of the lines.

Now look at the set of axes above. What do all the points on the blue line have in common?
Name 3 points on the green line.
What are the coordinates of the point which is on both the red and yellow lines?
Which line would the point (17,4) be on?