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Solution - Absolute value equations

Exact form:

x = \frac{13}{7}, - \frac{3}{11}

x=\frac{13}{7} , -\frac{3}{11}

Mixed number form:

x = 1 \frac{6}{7}, - \frac{3}{11}

x=1\frac{6}{7} , -\frac{3}{11}

Decimal form:

x = 1.857, - 0.273

x=1.857 , -0.273

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
$| 2 x + 8 | = | 9 x - 5 |$
without the absolute value bars:

$\| x \| = \| y \|$	$\| 2 x + 8 \| = \| 9 x - 5 \|$
$x = + y$	$(2 x + 8) = (9 x - 5)$
$x = - y$	$(2 x + 8) = - (9 x - 5)$
$+ x = y$	$(2 x + 8) = (9 x - 5)$
$- x = y$	$- (2 x + 8) = (9 x - 5)$

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:

$\| x \| = \| y \|$	$\| 2 x + 8 \| = \| 9 x - 5 \|$
$x = + y$ , $+ x = y$	$(2 x + 8) = (9 x - 5)$
$x = - y$ , $- x = y$	$(2 x + 8) = - (9 x - 5)$

2. Solve the two equations for x

11 additional steps

$(2 x + 8) = (9 x - 5)$

Subtract from both sides:

$(2 x + 8) - 9 x = (9 x - 5) - 9 x$

Group like terms:

$(2 x - 9 x) + 8 = (9 x - 5) - 9 x$

Simplify the arithmetic:

$- 7 x + 8 = (9 x - 5) - 9 x$

Group like terms:

$- 7 x + 8 = (9 x - 9 x) - 5$

Simplify the arithmetic:

$- 7 x + 8 = - 5$

Subtract from both sides:

$(- 7 x + 8) - 8 = - 5 - 8$

Simplify the arithmetic:

$- 7 x = - 5 - 8$

Simplify the arithmetic:

$- 7 x = - 13$

Divide both sides by :

$\frac{(- 7 x)}{- 7} = \frac{- 13}{- 7}$

Cancel out the negatives:

$\frac{7 x}{7} = \frac{- 13}{- 7}$

Simplify the fraction:

$x = \frac{- 13}{- 7}$

Cancel out the negatives:

$x = \frac{13}{7}$

10 additional steps

$(2 x + 8) = - (9 x - 5)$

Expand the parentheses:

$(2 x + 8) = - 9 x + 5$

Add to both sides:

$(2 x + 8) + 9 x = (- 9 x + 5) + 9 x$

Group like terms:

$(2 x + 9 x) + 8 = (- 9 x + 5) + 9 x$

Simplify the arithmetic:

$11 x + 8 = (- 9 x + 5) + 9 x$

Group like terms:

$11 x + 8 = (- 9 x + 9 x) + 5$

Simplify the arithmetic:

$11 x + 8 = 5$

Subtract from both sides:

$(11 x + 8) - 8 = 5 - 8$

Simplify the arithmetic:

$11 x = 5 - 8$

Simplify the arithmetic:

$11 x = - 3$

Divide both sides by :

$\frac{(11 x)}{11} = \frac{- 3}{11}$

Simplify the fraction:

$x = \frac{- 3}{11}$

3. List the solutions

$x = \frac{13}{7}, - \frac{3}{11}$
(2 solution(s))

4. Graph

Each line represents the function of one side of the equation:
$y = | 2 x + 8 |$
$y = | 9 x - 5 |$
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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