Solving inequalities
Properties of inequalities
Examples of solving single linear inequalities
Linear inequalities
A linear inequality is one that can be reduced to the standard form  ax + b > 0 where a, b Î R, and where other inequality signs like <, > and < can appear.
Solving inequalities
The solutions to an inequality are all values of x that make the inequality true. Usually the answer is a range of values of x that we plot on a number line.
We use similar method to solve linear inequalities as for solving linear equations:
- simplify both sides,
- bring all the terms with the variable on one side and the constants on the other side,
- and then multiply/divide both sides by the coefficient of the variable to get the solution while applying following properties:
Properties of inequalities
1. Adding or subtracting the same quantity from both sides of an inequality will not change the direction of the inequality sign.
2. Multiplying or dividing both sides of an inequality by a positive number leaves the inequality symbol unchanged.
3. Multiplying or dividing both sides of an inequality by the same negative number, the sense of the inequality changes, i.e., it reverses the direction of the inequality sign.
Examples of solving single linear inequalities
Solve each of the following inequalities, sketch the solution on the real number line and express the solution in interval notation.
 Example: x - 8 < 2x - 4 - x < 4 | · (-1) x > -4
 The solution of the inequality is every real number greater than  -4.
Example:     3(x - 2) > -2(1- x)
 Solution:     3x - 6 > -2 + 2x x > 4
 interval notation (4, oo)
The open interval (4, oo)  contains all real numbers between given endpoints, where round parentheses indicate exclusion of endpoints.
 Example: Solution:        -4x + 9 - 3x < 6 - 5 + 5x -12x < -8 x > 2/3
 interval notation
The half-closed (or half-open) interval contains all real numbers between given endpoints, where the square bracket indicates inclusion of the endpoint 2/3 and round parenthesis indicates exclusion of infinity.

Example:    (x - 3) · (x + 2) > 0

Solution:   The factor x - 3 has the zero at x = 3, is negative for x < 3 and is positive for x > 3, and
the factor x + 2 has the zero at x = -2, is negative for x < - 2 and is positive for x > -2,
as is shown in the table
 x - oo increases -2 increases 3 increases + oo x + 2 - 0 + + + x - 3 - - - 0 + (x - 3)(x + 2) + 0 - 0 +
Thus, the given inequality is satisfied for    - oo < x < - 2    or     3 < x < + oo
in the interval notation     (- oo , -2] U [3, + oo)
College algebra contents A