- You can
**specify****points**on a grid**using****coordinates**. These are most commonly are of the form (*x*,*y*). - You can
**specify**straight**lines**(as well as many**curves**) on a grid**using****equations**. These equations give you the relationship between the*x*and*y*coordinates of*every point on the line*. For example,*every*point on the line*y*=*x*has an*x*coordinate which equals its*y*coordinate. Such points include (1, 1), (2, 2), (3, 3) etc. but also (1.7, 1.7)… There are infinitely many points on the line, but the equation perfectly defines the line.

# A8a – Working with coordinates in all four quadrants

This topic is covered in lesson G7a – Coordinates.
When considering coordinates from an algebraic point of view, a key point to note is the following: