I have Learnt
On a number line, the graph of an inequality in one variable is the set of points that represent all solutions of the inequality. To graph an inequality in one variable are an open circle for < or > and a closed circle for ≤ or ≥. Dividing / multiplying each side of an inequality by a positive number produces an equivalent inequality. Dividing / multiplying each side of an inequality by a negative number and reversing the direction of the inequality symbol produces an equivalent inequality. A linear inequality in two variables, such as ax + by < c is the result of replacing the '=' sign in a linear equation with <, ≤, > or ≥. A solution of an inequality in two variables x and y is an ordered pair (x,y) that produces a true statement when the values of x and y are substituted into the inequality. The boundary line for an inequality in one variable is either vertical or horizontal. If an inequality has only the variable x, substitute the x-coordinate of the test point into the inequality. If an inequality has only the variable y, substitute the y-coordinate of the test point into the inequality. A solution of a system of linear inequalities is an ordered pair that is a solution of each inequality in the system. The graph of a system of linear inequalities is the graph of all solutions of the system.