6.2: Linear Inequalities
What if you had an inequality with an unknown variable like \begin{align*}x  12 > 5\end{align*}
Watch This
CK12 Foundation: 0602S Solving OneStep Inequalities (H264)
Guidance
To solve an inequality we must isolate the variable on one side of the inequality sign. To isolate the variable, we use the same basic techniques used in solving equations.
We can solve some inequalities by adding or subtracting a constant from one side of the inequality.
Example A
Solve the inequality and graph the solution set.
\begin{align*}x3<10\end{align*}
Solution
Starting inequality: \begin{align*}x3 < 10\end{align*}
Add 3 to both sides of the inequality: \begin{align*}x  3 + 3 < 10 + 3\end{align*}
Simplify: \begin{align*}x < 13\end{align*}
Example B
Solve the inequality and graph the solution set.
\begin{align*}x20 \le 14\end{align*}
Solution:
Starting inequality: \begin{align*}x  20 \le 14\end{align*}
Add 20 to both sides of the inequality: \begin{align*}x  20 + 20 \le 14 + 20\end{align*}
Simplify: \begin{align*}x \le 34\end{align*}
Solving Inequalities Using Multiplication and Division
We can also solve inequalities by multiplying or dividing both sides by a constant. For example, to solve the inequality \begin{align*}5x<3\end{align*}
However, something different happens when we multiply or divide by a negative number. We know, for example, that 5 is greater than 3. But if we multiply both sides of the inequality \begin{align*}5>3\end{align*}
This happens whenever we multiply or divide an inequality by a negative number, and so we have to flip the sign around to make the inequality true. For example, to multiply \begin{align*}2 < 4\end{align*}
The same principle applies when the inequality contains variables.
Example C
Solve the inequality.
\begin{align*}4x < 24\end{align*}
Solution:
Original problem: \begin{align*}4x < 24\end{align*}
Divide both sides by 4: \begin{align*}\frac{4x}{4} < \frac{24}{4}\end{align*}
Simplify: \begin{align*}x < 6\end{align*}
Example D
Solve the inequality.
\begin{align*}5x \le 21\end{align*}
Solution:
Original problem: \begin{align*}5x \le 21\end{align*}
Divide both sides by 5 : \begin{align*}\frac{5x}{5} \ge \frac{21}{5}\end{align*}
Simplify: \begin{align*}x \ge \frac{21}{5}\end{align*}
Watch this video for help with the Examples above.
CK12 Foundation: Solving OneStep Inequalities
Vocabulary
 The answer to an inequality is usually an interval of values.
 Solving inequalities works just like solving an equation. To solve, we isolate the variable on one side of the equation.
 When multiplying or dividing both sides of an inequality by a negative number, you need to reverse the inequality.
Guided Practice
Solve each inequality.
a) \begin{align*}x+8 \le 7\end{align*}
b) \begin{align*}x+4 > 13\end{align*}
c) \begin{align*}\frac{x}{25} < \frac{3}{2}\end{align*}
d) \begin{align*}\frac{x}{7} \ge 9\end{align*}
Solutions:
a) Starting inequality: \begin{align*}x+8 \le 7\end{align*}
Subtract 8 from both sides of the inequality: \begin{align*}x + 8  8 \le 7  8\end{align*}
Simplify: \begin{align*}x\le 15\end{align*}
b) Starting inequality: \begin{align*}x+4 > 13\end{align*}
Subtract 4 from both sides of the inequality: \begin{align*}x + 4  4 > 13  4\end{align*}
Simplify: \begin{align*}x > 9\end{align*}
c) Original problem: \begin{align*}\frac{x}{25} < \frac{3}{2}\end{align*}
Multiply both sides by 25: \begin{align*}25 \cdot \frac{x}{25} < \frac{3}{2} \cdot 25\end{align*}
Simplify: \begin{align*}x < \frac{75}{2}\end{align*}
d) Original problem: \begin{align*}\frac{x}{7} \ge 9\end{align*}
Multiply both sides by 7: \begin{align*}7 \cdot \frac{x}{7} \le 9 \cdot (7)\end{align*}
Simplify: \begin{align*}x \le 63\end{align*}
Explore More
For 18, solve each inequality and graph the solution on the number line.

\begin{align*}x5 < 35\end{align*}
x−5<35 
\begin{align*}x+15 \ge 60\end{align*}
x+15≥−60 
\begin{align*}x2 \le 1\end{align*}
x−2≤1 
\begin{align*}x8 > 20\end{align*}
x−8>−20 
\begin{align*}x+11>13\end{align*}
x+11>13 
\begin{align*}x+65<100\end{align*}
x+65<100 
\begin{align*}x32 \le 0\end{align*}
x−32≤0 
\begin{align*}x+68 \ge 75\end{align*}
x+68≥75
For 912, solve each inequality. Write the solution as an inequality and graph it.

\begin{align*}3x \le 6\end{align*}
3x≤6  \begin{align*}\frac{x}{5} > \frac{3}{10}\end{align*}
 \begin{align*}10x>250\end{align*}
 \begin{align*}\frac{x}{7} \ge 5\end{align*}
distributive property
The distributive property states that the product of an expression and a sum is equal to the sum of the products of the expression and each term in the sum. For example, .Linear Inequality
Linear inequalities are inequalities that can be written in one of the following four forms: , or .Image Attributions
Description
Learning Objectives
Here you'll learn how to solve inequalities by isolating the variable on one side of the inequality sign. You'll also learn how to graph their solution set.
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Date Created:
Aug 13, 2012Last Modified:
Sep 27, 2015Vocabulary
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