Linear Inequalities


Linear Inequalities


Solving a linear inequality is similar to solving a linear equation. The only difference is that when you multiply or divide both sides by a negative number, you must change the direction of the inequality.


      6 > 4 
-1(6) < -1(4) 
    -6 < -4


To graph an inequality, mark its position and direction on a number line.

x < 3


The open circle indicates that the value of 3 is not part of the inequality.


x < 3


The closed circle now indicates that the value of 3 is part of the inequality.


To express an inequality in interval notation:

  • Include the span of numbers included in the group from left to right, separated by a comma.
  • Use parenthesis next to a number that is excluded from the group. Use a bracket when the number is included in the group.
  • Use the infinity or negative infinity symbols to denote when the group goes on indefinitely.  Always use round parentheses symbols with infinity.

x < 3

(-, 3)


x < 3

(-, 3]


Example

7 - 4x < -13


As you would with an equation, add or subtract terms to get all variables on one side and all constants on the other.

7 - 4x - 7 < -13 - 7

         -4x < -20

Now divide both sides by the coefficient of x.  (Careful, the coefficient in this example is negative!)

 -4x / -4 > -20 / -4