Lesson Objectives
  • Demonstrate the ability to solve a radical equation
  • Learn how to solve a radical inequality

How to Solve a Radical Inequality


Solving radical inequalities can be quite tedious depending on the type of problem that you encounter. The method that is described below is not necessarily the fastest, especially if you have an easy problem. The benefit of this method is that it will work for any scenario.

Solving a Radical Inequality:

  • Find any domain restrictions
  • Replace the inequality symbol with an equality symbol
    • Solve the resulting equation
    • The solution gives us the critical values or boundaries
  • Split the number line up into intervals based on the critical values and domain restrictions
  • Test numbers in each interval to obtain your solution set
Example 1: Solve each inequality $$-5\sqrt{2x+12}+ 2 > -18$$ Step 1) Find any domain restrictions:
Set your radicand (2x + 12) as greater than or equal to zero and solve the inequality: $$2x + 12 ≥ 0$$ $$x ≥ -6$$ Step 2) Replace the inequality symbol with an equality symbol and solve the resulting equation: $$-5\sqrt{2x + 12}+ 2=-18$$ $$x=2$$ This solution gives us a boundary. We can use it to split the number line up into three intervals. A region that is less than -6, where no values will work due to the domain restriction. A region that is between -6 and 2, and a region that is greater than 2. For the numbers -6 and 2, we will consider them separately. number line split into three intervals Step 3) Test numbers in each interval to obtain your solution set:
We know that nothing in interval A (values less than -6) works due to the domain restriction.
For interval B we can test 0: $$-5\sqrt{2(0) + 12}+ 2 > -18$$ $$-5\sqrt{12}+ 2 > -18$$ $$-10\sqrt{3}> -20$$ Since this statement is true, we can conclude that any value from -6 up to but not including 2 will work. 2 is excluded here because we have a non-strict inequality. Testing any value in region C, where values are larger than 2 will result in a false statement. We will report our answer as: $$-6 ≤ x < 2$$ $$[-6, 2)$$ number line split into three intervals

Skills Check:

Example #1

Solve each inequality. $$\sqrt{2x - 4}+ 9 ≤ 11$$

Please choose the best answer.

A
$$x ≥ 4$$
B
$$2 < x ≤ 4$$
C
$$2 ≤ x ≤ 4$$
D
$$x ≤ 2$$
E
$$x ≤ 2 \hspace{.1em}\text{or}\hspace{.1em}x ≥ 4$$

Example #2

Solve each inequality. $$\sqrt{x + 9}> \sqrt{3 - 2x}$$

Please choose the best answer.

A
$$-\frac{3}{2}≤ x < 2$$
B
$$x > \frac{3}{2}$$
C
$$x ≤ -2$$
D
$$-2 < x ≤ \frac{3}{2}$$
E
$$-2 ≤ x < \frac{3}{2}$$

Example #3

Solve each inequality. $$5 + \sqrt{3x - 8}≥ 7$$

Please choose the best answer.

A
$$x ≤ \frac{8}{3}$$
B
$$x ≥ \frac{8}{3}$$
C
$$-2 ≤ x ≤ 4$$
D
$$x ≥ 4$$
E
$$x ≤ 4$$
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