Precalculus (6th Edition) Blitzer

We know that a linear equation is an algebraic equation in which each term is either a constant or the product of a constant and a single variable. Let us take an example, The equation $ax+by=c$ is a standard form of a linear equation. Other examples are $x=1,\ y=0,2x+3y=4\text{ and }x+y=3$ etc. All of these equations are in the form of linear equations.