Standard form is another alternative to Slope-Intercept and Point-Slope forms, and has the format Ax + By = C, where A, B, and C are real numbers
and A is not negative. The Standard Form has its uses, it can more easily be written from word problem in some cases, for example, given x dogs
and y people with 20 total legs. This could be written as 4x + 2y = 20, as each dog has 4 legs and each person has 2. So the equation reads as
"4 legs per dog times the number of dogs plus 2 legs per person times the number of people equals the total number of legs". The Standard Form will
also be useful when solving systems of linear equations (see
Chapter 7). Also of note, when A = 0, the equation models
a horizontal line, and if B = 0, the equation represents a vertical line.