Linear equations in two variables. If a, b, and r are real numbers (and if a and b are not both equal to 0), then ax+by = r is called a linear equation in two variables. (The “two variables” are the x and the y.) The numbers a and b are called the coefficients of the equation ax+by = r. The equation is called linear because the equation is of the first degree. A solution is an ordered pair of real numbers which satisfies the equation. Some of the concepts discussed in the chapter via the listed exercises consist of Solution of a Linear Equation, Simultaneous Linear Equations in Two Variables, Solution of a Given System of Two Simultaneous Equations, Consistent and Inconsistent Systems of Linear Equations and more.