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How to Solve Inequalities in GeoGebra

You can use GeoGebra to solve systems of inequalities. Type >= to enter , and <= to enter .

GeoGebra Instruction 1

Solution in CAS

1.
Open CAS under GeoGebra icon View in GeoGebra icon Menu.
2.
Enter the inequality and press Solve GeoGebra icon to get an exact solution .

Example 1

The image below shows what it looks like in GeoGebra if you solve the inequality x2 4 3x by following the instructions above.

Note! If GeoGebra returns {}, then the inequality has no solution. If GeoGebra returns true, then the inequality is always true. If GeoGebra returns false, then the expression is never true for any x. If GeoGebra returns ?, you have pressed Solve Numerically GeoGebra icon. GeoGebra does not allow this. You must use Solve GeoGebra icon.

Screenshot of GeoGebra showing the solutions of three inequalities

GeoGebra Instruction 2

Solution in Graphics View

1.
Open Graphics View in GeoGebra icon View.
2.
Enter the left-hand side of the inequality in Algebra View and press Enter.
3.
Enter the right-hand side of the inequality in Algebra View and press Enter.
4.
Select the Intersect GeoGebra icon tool and click the two graphs to find any possible intersections. You’re going to use the intersection points later.

If you don’t get any intersection points, then your inequality is either always true, or never true. Continue to the next step to find out which one of these is the case for your inequality.

5.
If the inequality contains the symbols > or , type f(x)>g(x) in Algebra View. If the inequality contains the symbols < or , type f(x)<g(x) in Algebra View. Then press Enter.

The solution is the union of all the intervals of the x-axis that are covered in blue.

If you didn’t get any intersection points in Step 4, the Graphics View window should be covered entirely in blue if your inequality is always true (x ), or not covered at all if it’s never true (x ).

If you did get intersection points in Step 4, use the x-coordinates of the intersection points as the boundaries of the intervals. If the blue area extends indefinitely to the right, use instead, or if it extends indefinitely to the left, use instead. If the equation uses or , use brackets, i.e. ( []) at the boundary points, otherwise use regular parentheses, ().

Screenshot of GeoGebra highlighting where a parabola lies above a line

The picture shows the area where the graph of f(x) = x2 4 lies above the graph of g(x) = 3x in the coordinate system. This means that the y-value of f is greater than the y-value of g in the shaded area. From the image you can see that f(x) > g(x) when x (,1) (4,).

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