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# Absolute Value Equations

## Equations may have two solutions due to the absolute value operation

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Practice Absolute Value Equations
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Solutions to Absolute Value Equations

Solve for the variable in the equation: \begin{align*}|3x+1|=4\end{align*}

### Guidance

Recall that a linear equation relates mathematical expressions with an equals sign. To solve an absolute linear equation you have to remember the same rules that you have used to solve linear equations with one variable. The difference with absolute value equations is there will often be two solutions instead of just one solution. Consider the following equations:

1.

This means that x can be 5 or x can be –5. This is because \begin{align*}|5|=|-5|=5\end{align*}.

2.

This means that \begin{align*}x+1\end{align*} can be 7 or \begin{align*}x+1\end{align*} can be –7. This is because \begin{align*}|7|=|-7|=7\end{align*}.

3.

The absolute value of \begin{align*}x\end{align*} can never be equal to a negative number. Therefore if an absolute value equation is equal to a negative number, there is no solution.

#### Example A

\begin{align*}|d+3|=2.1\end{align*}

Solution: Set up two equations to solve. You know that either \begin{align*}d+3=2.1\end{align*} OR \begin{align*}d+3=-2.1\end{align*}. The quantity inside the absolute value signs could be either the positive or negative of the value on the right side.

Solutions \begin{align*}= 0.9, -5.1\end{align*}

#### Example B

\begin{align*}|2(z+4)|=|5|\end{align*}

Solution: First of all, you know that \begin{align*}|5|=5\end{align*}. Now, set up two equations to solve. You know that either \begin{align*}2(z+4)=5\end{align*} OR \begin{align*}2(z+4)=-5\end{align*}.

Solutions \begin{align*}= \frac{-3}{2},\frac{-13}{2}\end{align*}

#### Example C

\begin{align*}\big|\frac{1}{2}x+3\big|=\big|\frac{4}{5}\big|\end{align*}

Solution: First of all, you know that \begin{align*}\big|\frac{4}{5}\big|=\frac{4}{5}\end{align*}. Now, set up two equations to solve. You know that either \begin{align*}\frac{1}{2}x+3=\frac{4}{5}\end{align*} OR \begin{align*}\frac{1}{2}x+3=-\frac{4}{5}\end{align*}.

Solutions \begin{align*}= \frac{-22}{5},\frac{-38}{5}\end{align*}

#### Concept Problem Revisited

Solve for the variable in the expression: \begin{align*}|3x+1|=4\end{align*}

Because \begin{align*}|3x+1|=4\end{align*}, the expression \begin{align*}3x + 1\end{align*} is equal to 4 or –4.

Just like with regular linear equations, you can check both answers.

### Vocabulary

Absolute Value
Absolute value in the real number system is the distance from zero on the number line. It is always a positive number and is represented using the symbol \begin{align*}|x|\end{align*}.
Linear Equation
A linear equation relates mathematical expressions with the equals sign.

### Guided Practice

Solve each equation.

1. \begin{align*}|4a-2|=3\end{align*}

2. \begin{align*}|2b-8|-3=4\end{align*}

3. \begin{align*}\big|\frac{1}{2}c-5\big|=3\end{align*}

1. The solutions are \begin{align*} \frac{5}{4},\frac{-1}{4}\end{align*}. Here are the steps:

2. The solutions are \begin{align*} \frac{15}{2},\frac{1}{2}\end{align*}. First, isolate the part of the equation with the absolute value sign by adding 3 to both sides. The new equation is \begin{align*}|2b-8|=7\end{align*}. Then, set up two equations and solve.

3. The solutions are \begin{align*} 16, 4\end{align*}. Here are the steps to solve:

### Practice

Solve each of the following absolute value linear equations.

1. \begin{align*}|t+2|=4\end{align*}
2. \begin{align*}|r-2|=7\end{align*}
3. \begin{align*}|5-k|=6\end{align*}
4. \begin{align*}|6-y|=12\end{align*}
5. \begin{align*}-6=|1-b|\end{align*}
6. \begin{align*}\big|\frac{1}{5}x-3\big|=1\end{align*}
7. \begin{align*}\big|\frac{1}{2}(r-3)\big|=2\end{align*}
8. \begin{align*}\big|\frac{1}{3}(f+1)\big|=5\end{align*}
9. \begin{align*}|3d-11|=-2\end{align*}
10. \begin{align*}|5w+9|-6=68\end{align*}
11. \begin{align*}|5(2t+5)+3(t-1)|=-3\end{align*}
12. \begin{align*}|2.24x-24.63|=2.25\end{align*}
13. \begin{align*}|6(5j-3)+2|=14\end{align*}
14. \begin{align*}|7g-8(g+3)|=1\end{align*}
15. \begin{align*}|e+4(e+3)|=17\end{align*}

### Answers for Explore More Problems

To view the Explore More answers, open this PDF file and look for section 2.13.

### Vocabulary Language: English

Absolute Value

Absolute Value

The absolute value of a number is the distance the number is from zero. Absolute values are never negative.
linear equation

linear equation

A linear equation is an equation between two variables that produces a straight line when graphed.