When the equal sign in a quadratic or linear equation is replaced with an inequality sign, a quadratic inequality in one variable is formed. It also determines the domain and range for one equation. It is a very useful when having graphing skills. I have a example of linear and quadratic equation each above. I find determining whether this equation is true or false hard as I have to plug in random points on the graph, which isn’t labelled, which also determine the shaded parts, depending on whether it is true or false.