How do you work out the equation for a line?

In order to work out the equation for a line, you need the gradient of the line and the coordinates of a point on the line. To find the gradient on the line, you look at two points on the line and calculate the rise over the run. If a line goes up vertically by 3 between two points on the line but only goes right horizontally by 1, the rise over the run is 3/1 so the gradient is 3.

Using one of these points and the gradient you can work out the equation of the line with the following formula. 

y-y1=m(x-x1) where y1 and x1 are the coordinates of the point on the line and m is the gradient. Simply rearrange to make y the subject of this equation and you will have the equation of the line given in its normal form.