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Solution - Absolute value equations

Exact form:

x = - 4, - 12

x=-4 , -12

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
$| - 2 x - 4 | = | 3 x + 16 |$
without the absolute value bars:

$\| x \| = \| y \|$	$\| - 2 x - 4 \| = \| 3 x + 16 \|$
$x = + y$	$(- 2 x - 4) = (3 x + 16)$
$x = - y$	$(- 2 x - 4) = - (3 x + 16)$
$+ x = y$	$(- 2 x - 4) = (3 x + 16)$
$- x = y$	$- (- 2 x - 4) = (3 x + 16)$

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:

$\| x \| = \| y \|$	$\| - 2 x - 4 \| = \| 3 x + 16 \|$
$x = + y$ , $+ x = y$	$(- 2 x - 4) = (3 x + 16)$
$x = - y$ , $- x = y$	$(- 2 x - 4) = - (3 x + 16)$

2. Solve the two equations for x

13 additional steps

$(- 2 x - 4) = (3 x + 16)$

Subtract from both sides:

$(- 2 x - 4) - 3 x = (3 x + 16) - 3 x$

Group like terms:

$(- 2 x - 3 x) - 4 = (3 x + 16) - 3 x$

Simplify the arithmetic:

$- 5 x - 4 = (3 x + 16) - 3 x$

Group like terms:

$- 5 x - 4 = (3 x - 3 x) + 16$

Simplify the arithmetic:

$- 5 x - 4 = 16$

Add to both sides:

$(- 5 x - 4) + 4 = 16 + 4$

Simplify the arithmetic:

$- 5 x = 16 + 4$

Simplify the arithmetic:

$- 5 x = 20$

Divide both sides by :

$\frac{(- 5 x)}{- 5} = \frac{20}{- 5}$

Cancel out the negatives:

$\frac{5 x}{5} = \frac{20}{- 5}$

Simplify the fraction:

$x = \frac{20}{- 5}$

Move the negative sign from the denominator to the numerator:

$x = \frac{- 20}{5}$

Find the greatest common factor of the numerator and denominator:

$x = \frac{(- 4 \cdot 5)}{(1 \cdot 5)}$

Factor out and cancel the greatest common factor:

$x = - 4$

8 additional steps

$(- 2 x - 4) = - (3 x + 16)$

Expand the parentheses:

$(- 2 x - 4) = - 3 x - 16$

Add to both sides:

$(- 2 x - 4) + 3 x = (- 3 x - 16) + 3 x$

Group like terms:

$(- 2 x + 3 x) - 4 = (- 3 x - 16) + 3 x$

Simplify the arithmetic:

$x - 4 = (- 3 x - 16) + 3 x$

Group like terms:

$x - 4 = (- 3 x + 3 x) - 16$

Simplify the arithmetic:

$x - 4 = - 16$

Add to both sides:

$(x - 4) + 4 = - 16 + 4$

Simplify the arithmetic:

$x = - 16 + 4$

Simplify the arithmetic:

$x = - 12$

3. List the solutions

$x = - 4, - 12$
(2 solution(s))

4. Graph

Each line represents the function of one side of the equation:
$y = | - 2 x - 4 |$
$y = | 3 x + 16 |$
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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