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Solution - Absolute value equations

Exact form:

x = - \frac{12}{5}, \frac{12}{11}

x=-\frac{12}{5} , \frac{12}{11}

Mixed number form:

x = - 2 \frac{2}{5}, 1 \frac{1}{11}

x=-2\frac{2}{5} , 1\frac{1}{11}

Decimal form:

x = - 2.4, 1.091

x=-2.4 , 1.091

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
$| 3 x - 12 | = | 8 x |$
without the absolute value bars:

$\| x \| = \| y \|$	$\| 3 x - 12 \| = \| 8 x \|$
$x = + y$	$(3 x - 12) = (8 x)$
$x = - y$	$(3 x - 12) = - (8 x)$
$+ x = y$	$(3 x - 12) = (8 x)$
$- x = y$	$- (3 x - 12) = (8 x)$

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:

$\| x \| = \| y \|$	$\| 3 x - 12 \| = \| 8 x \|$
$x = + y$ , $+ x = y$	$(3 x - 12) = (8 x)$
$x = - y$ , $- x = y$	$(3 x - 12) = - (8 x)$

2. Solve the two equations for x

10 additional steps

$(3 x - 12) = 8 x$

Subtract from both sides:

$(3 x - 12) - 8 x = (8 x) - 8 x$

Group like terms:

$(3 x - 8 x) - 12 = (8 x) - 8 x$

Simplify the arithmetic:

$- 5 x - 12 = (8 x) - 8 x$

Simplify the arithmetic:

$- 5 x - 12 = 0$

Add to both sides:

$(- 5 x - 12) + 12 = 0 + 12$

Simplify the arithmetic:

$- 5 x = 0 + 12$

Simplify the arithmetic:

$- 5 x = 12$

Divide both sides by :

$\frac{(- 5 x)}{- 5} = \frac{12}{- 5}$

Cancel out the negatives:

$\frac{5 x}{5} = \frac{12}{- 5}$

Simplify the fraction:

$x = \frac{12}{- 5}$

Move the negative sign from the denominator to the numerator:

$x = \frac{- 12}{5}$

7 additional steps

$(3 x - 12) = - 8 x$

Add to both sides:

$(3 x - 12) + 12 = (- 8 x) + 12$

Simplify the arithmetic:

$3 x = (- 8 x) + 12$

Add to both sides:

$(3 x) + 8 x = ((- 8 x) + 12) + 8 x$

Simplify the arithmetic:

$11 x = ((- 8 x) + 12) + 8 x$

Group like terms:

$11 x = (- 8 x + 8 x) + 12$

Simplify the arithmetic:

$11 x = 12$

Divide both sides by :

$\frac{(11 x)}{11} = \frac{12}{11}$

Simplify the fraction:

$x = \frac{12}{11}$

3. List the solutions

$x = - \frac{12}{5}, \frac{12}{11}$
(2 solution(s))

4. Graph

Each line represents the function of one side of the equation:
$y = | 3 x - 12 |$
$y = | 8 x |$
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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