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. An equation of the form ax + by + c = 0; where a, b, c are real numbers, a, b are not equal to zero, and x, y are variable, is called a linear equation in two variables. For example, 2x + 3y = 0 and 2 – x + y = 0. This chapter consists of topics like Linear Equations in two variables, solution of a linear equation, Graph of a linear equation in two variables and equations of lines parallel to the X-axis and Y-axis.