# Coordinate Geometry

- Author:
- pirsquared

## Key Facts

You need to know the following important formulae and rules:

- Distance between two points is found by Pythagoras' theorem:
- Coordinates of the midpoint of a line are the midpoints between the two coordinates:
- Gradient of a line is
**change in y ÷ change in x**(or) - If two lines are perpendicular,
- The most commonly used equation of a straight line is
- You can also use
if you have two known points. - Points of intersection (where two lines cross) can be found using simultaneous equations.

*Test Yourself*below to practise finding distances, gradients, midpoints, perpendicular gradients and equations of straight lines.