Standard Form of a Line

The standard form of a line is Ax + By = C. The slope-intercept form,

y = mx + b

cannot be used for undefined m (vertical lines), whereas the standard can.

This is by setting A = 0.

We need two points to define a line. One way is to use the standard form:

•	One point is x =0. We can then solve for y, and get our point.

•	The second point we can get by setting y = 0.

Using the y-intercept and the x-intercept is very helpful, except:

•	This trick will not work if a line goes through the origin. In this case, setting x = 0 will give us only one point, and we have to choose an arbitrary x and solve for y.

•	The slope-intercept form does not work for vertical lines. (Why not?)