The graphs of quadratic inequalities follow the same general relationship. Greater than inequalities are the region above the equation's graph and less than inequalities are made up by the region underneath the graph of the equation.
What is the solution of a quadratic inequality?
Below, you will learn a formula for solving quadratic inequalities. First, it's important to try to understand what a quadratic inequality is and what its solution is. So let us explore a graphical solution for a quadratic inequality.
We will examine the quadratic inequality $$ y > x^2 -1 $$ .
The yellow region represents the graph of the quadratic inequality.
The red line segment from $$ (-1, 2) $$ to $$ (1, 2) $$ represents the solution itself, graphically.
The solution, graphically, is always where the graph of the inequality overlaps with the x axis .
Diagram 7
The same basic concepts apply to quadratic inequalities like $$ y < x^2 -1 $$ from digram 8. This is the same quadratic equation, but the inequality has been changed to $$ \red < $$.
In this case, we have drawn the graph of inequality using a pink color. And that represents the graph of the inequality.
The solution , graphically, is always where the graph of the inequality overlaps with the x axis .
Diagram 8
General Formula
for Solutions of Quadratic Inequalities
The table below represents two general formulas that express the solution of a quadratic inequality of a parabola that opens upwards (ie a > 0) whose roots are r1 and r2.
The Greater Than Inequality
0 > ax² + bx + c
Solution: {x| r1 < X < r2}
The Less Than Inequality
0 < ax² + bx + c
Solution: {x| x < r1 or x > r2}
We can reproduce these general formula for inequalities that include the quadratic itself (ie ≥ and ≤).
