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Solution - Absolute value equations

Exact form:

x = - 6, - 3

x=-6 , -3

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

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

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:

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

2. Solve the two equations for x

7 additional steps

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

Add to both sides:

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

Simplify the arithmetic:

$2 x = (- 3 x - 12) + 3 x$

Group like terms:

$2 x = (- 3 x + 3 x) - 12$

Simplify the arithmetic:

$2 x = - 12$

Divide both sides by :

$\frac{(2 x)}{2} = \frac{- 12}{2}$

Simplify the fraction:

$x = \frac{- 12}{2}$

Find the greatest common factor of the numerator and denominator:

$x = \frac{(- 6 \cdot 2)}{(1 \cdot 2)}$

Factor out and cancel the greatest common factor:

$x = - 6$

10 additional steps

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

Expand the parentheses:

$- x = 3 x + 12$

Subtract from both sides:

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

Simplify the arithmetic:

$- 4 x = (3 x + 12) - 3 x$

Group like terms:

$- 4 x = (3 x - 3 x) + 12$

Simplify the arithmetic:

$- 4 x = 12$

Divide both sides by :

$\frac{(- 4 x)}{- 4} = \frac{12}{- 4}$

Cancel out the negatives:

$\frac{4 x}{4} = \frac{12}{- 4}$

Simplify the fraction:

$x = \frac{12}{- 4}$

Move the negative sign from the denominator to the numerator:

$x = \frac{- 12}{4}$

Find the greatest common factor of the numerator and denominator:

$x = \frac{(- 3 \cdot 4)}{(1 \cdot 4)}$

Factor out and cancel the greatest common factor:

$x = - 3$

3. List the solutions

$x = - 6, - 3$
(2 solution(s))

4. Graph

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