Explain Linear Equations ?

Set of ordered pairs of numbers
A set is an undefined term and we describe it as a "well defined" collection. We use the symbol "{ }" to denote "a set" and the symbol "|" inside "{ }" to denote "such that". Consider the set of ordered pairs of numbers {(2,7), (2,8), (3,7), (3,8)}. We can rewrite the set in the form {(x,y)| x is either 2 or 3 and y is either 7 or 8}. In the figure, the set of elements {(2,7), (2,8), (3,7), (3,8)} is pictured as A, B, C, and D. The points A, B, C, and D are called the graph of the set of elements {(2,7), (2,8), (3,7), (3,8)}.

Definition
The graph of a set of ordered pairs of numbers is the set of points whose coordinates are members of the original set.

Set of elements of an equation

Let's consider the following set {(x,y) | y = 2x + 1}. We can express the above set as the set of elements {...(-1,-1), (0,1), (1,3), (2,5), (3,7)...} where the set of pairs of values must satisfy the equation y = 2x + 1.