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Solution - Absolute value equations

Exact form:

x = - \frac{5}{3}, - \frac{3}{13}

x=-\frac{5}{3} , -\frac{3}{13}

Mixed number form:

x = - 1 \frac{2}{3}, - \frac{3}{13}

x=-1\frac{2}{3} , -\frac{3}{13}

Decimal form:

x = - 1.667, - 0.231

x=-1.667 , -0.231

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
$| 5 x - 1 | = | 8 x + 4 |$
without the absolute value bars:

$\| x \| = \| y \|$	$\| 5 x - 1 \| = \| 8 x + 4 \|$
$x = + y$	$(5 x - 1) = (8 x + 4)$
$x = - y$	$(5 x - 1) = - (8 x + 4)$
$+ x = y$	$(5 x - 1) = (8 x + 4)$
$- x = y$	$- (5 x - 1) = (8 x + 4)$

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:

$\| x \| = \| y \|$	$\| 5 x - 1 \| = \| 8 x + 4 \|$
$x = + y$ , $+ x = y$	$(5 x - 1) = (8 x + 4)$
$x = - y$ , $- x = y$	$(5 x - 1) = - (8 x + 4)$

2. Solve the two equations for x

11 additional steps

$(5 x - 1) = (8 x + 4)$

Subtract from both sides:

$(5 x - 1) - 8 x = (8 x + 4) - 8 x$

Group like terms:

$(5 x - 8 x) - 1 = (8 x + 4) - 8 x$

Simplify the arithmetic:

$- 3 x - 1 = (8 x + 4) - 8 x$

Group like terms:

$- 3 x - 1 = (8 x - 8 x) + 4$

Simplify the arithmetic:

$- 3 x - 1 = 4$

Add to both sides:

$(- 3 x - 1) + 1 = 4 + 1$

Simplify the arithmetic:

$- 3 x = 4 + 1$

Simplify the arithmetic:

$- 3 x = 5$

Divide both sides by :

$\frac{(- 3 x)}{- 3} = \frac{5}{- 3}$

Cancel out the negatives:

$\frac{3 x}{3} = \frac{5}{- 3}$

Simplify the fraction:

$x = \frac{5}{- 3}$

Move the negative sign from the denominator to the numerator:

$x = \frac{- 5}{3}$

10 additional steps

$(5 x - 1) = - (8 x + 4)$

Expand the parentheses:

$(5 x - 1) = - 8 x - 4$

Add to both sides:

$(5 x - 1) + 8 x = (- 8 x - 4) + 8 x$

Group like terms:

$(5 x + 8 x) - 1 = (- 8 x - 4) + 8 x$

Simplify the arithmetic:

$13 x - 1 = (- 8 x - 4) + 8 x$

Group like terms:

$13 x - 1 = (- 8 x + 8 x) - 4$

Simplify the arithmetic:

$13 x - 1 = - 4$

Add to both sides:

$(13 x - 1) + 1 = - 4 + 1$

Simplify the arithmetic:

$13 x = - 4 + 1$

Simplify the arithmetic:

$13 x = - 3$

Divide both sides by :

$\frac{(13 x)}{13} = \frac{- 3}{13}$

Simplify the fraction:

$x = \frac{- 3}{13}$

3. List the solutions

$x = - \frac{5}{3}, - \frac{3}{13}$
(2 solution(s))

4. Graph

Each line represents the function of one side of the equation:
$y = | 5 x - 1 |$
$y = | 8 x + 4 |$
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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