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Solution - Absolute value equations

Exact form:

x = \frac{7}{4}, - \frac{11}{6}

x=\frac{7}{4} , -\frac{11}{6}

Mixed number form:

x = 1 \frac{3}{4}, - 1 \frac{5}{6}

x=1\frac{3}{4} , -1\frac{5}{6}

Decimal form:

x = 1.75, - 1.833

x=1.75 , -1.833

See steps

Step-by-step explanation

1. Rewrite the equation without absolute value bars

Use the rules:
$| x | = | y |$ → $x = \pm y$ and $| x | = | y |$ → $\pm x = y$
to write all four options of the equation
$| x + 9 | = | 5 x + 2 |$
without the absolute value bars:

$\| x \| = \| y \|$	$\| x + 9 \| = \| 5 x + 2 \|$
$x = + y$	$(x + 9) = (5 x + 2)$
$x = - y$	$(x + 9) = - (5 x + 2)$
$+ x = y$	$(x + 9) = (5 x + 2)$
$- x = y$	$- (x + 9) = (5 x + 2)$

When simplified, equations $x = + y$ and $+ x = y$ are the same and equations $x = - y$ and $- x = y$ are the same, so we end up with only 2 equations:

$\| x \| = \| y \|$	$\| x + 9 \| = \| 5 x + 2 \|$
$x = + y$ , $+ x = y$	$(x + 9) = (5 x + 2)$
$x = - y$ , $- x = y$	$(x + 9) = - (5 x + 2)$

2. Solve the two equations for x

11 additional steps

$(x + 9) = (5 x + 2)$

Subtract from both sides:

$(x + 9) - 5 x = (5 x + 2) - 5 x$

Group like terms:

$(x - 5 x) + 9 = (5 x + 2) - 5 x$

Simplify the arithmetic:

$- 4 x + 9 = (5 x + 2) - 5 x$

Group like terms:

$- 4 x + 9 = (5 x - 5 x) + 2$

Simplify the arithmetic:

$- 4 x + 9 = 2$

Subtract from both sides:

$(- 4 x + 9) - 9 = 2 - 9$

Simplify the arithmetic:

$- 4 x = 2 - 9$

Simplify the arithmetic:

$- 4 x = - 7$

Divide both sides by :

$\frac{(- 4 x)}{- 4} = \frac{- 7}{- 4}$

Cancel out the negatives:

$\frac{4 x}{4} = \frac{- 7}{- 4}$

Simplify the fraction:

$x = \frac{- 7}{- 4}$

Cancel out the negatives:

$x = \frac{7}{4}$

10 additional steps

$(x + 9) = - (5 x + 2)$

Expand the parentheses:

$(x + 9) = - 5 x - 2$

Add to both sides:

$(x + 9) + 5 x = (- 5 x - 2) + 5 x$

Group like terms:

$(x + 5 x) + 9 = (- 5 x - 2) + 5 x$

Simplify the arithmetic:

$6 x + 9 = (- 5 x - 2) + 5 x$

Group like terms:

$6 x + 9 = (- 5 x + 5 x) - 2$

Simplify the arithmetic:

$6 x + 9 = - 2$

Subtract from both sides:

$(6 x + 9) - 9 = - 2 - 9$

Simplify the arithmetic:

$6 x = - 2 - 9$

Simplify the arithmetic:

$6 x = - 11$

Divide both sides by :

$\frac{(6 x)}{6} = \frac{- 11}{6}$

Simplify the fraction:

$x = \frac{- 11}{6}$

3. List the solutions

$x = \frac{7}{4}, - \frac{11}{6}$
(2 solution(s))

4. Graph

Each line represents the function of one side of the equation:
$y = | x + 9 |$
$y = | 5 x + 2 |$
The equation is true where the two lines cross.

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Why learn this

We encounter absolute values almost daily. For example: If you walk 3 miles to school, do you also walk minus 3 miles when you go back home? The answer is no because distances use absolute value. The absolute value of the distance between home and school is 3 miles, there or back.
In short, absolute values help us deal with concepts like distance, ranges of possible values, and deviation from a set value.

Solution - Absolute value equations

Step-by-step explanation

1. Rewrite the equation without absolute value bars

2. Solve the two equations for x

3. List the solutions

4. Graph

Why learn this

Terms and topics

Related links

Solution - Absolute value equations

Step-by-step explanation

1. Rewrite the equation without absolute value bars

2. Solve the two equations for x

3. List the solutions

4. Graph

Why learn this

Terms and topics

Related links

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