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Solution - Absolute value equations

Exact form:

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

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

Mixed number form:

x = 12, 2 \frac{2}{5}

x=12 , 2\frac{2}{5}

Decimal form:

x = 12, 2.4

x=12 , 2.4

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

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

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:

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

2. Solve the two equations for x

8 additional steps

$3 \cdot (x - 4) = 2 x$

Expand the parentheses:

$3 x + 3 \cdot - 4 = 2 x$

Simplify the arithmetic:

$3 x - 12 = 2 x$

Subtract from both sides:

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

Group like terms:

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

Simplify the arithmetic:

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

Simplify the arithmetic:

$x - 12 = 0$

Add to both sides:

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

Simplify the arithmetic:

$x = 0 + 12$

Simplify the arithmetic:

$x = 12$

10 additional steps

$3 \cdot (x - 4) = - (2 x)$

Expand the parentheses:

$3 x + 3 \cdot - 4 = - (2 x)$

Simplify the arithmetic:

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

Add to both sides:

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

Group like terms:

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

Simplify the arithmetic:

$5 x - 12 = (- 2 x) + 2 x$

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 :

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

Simplify the fraction:

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

3. List the solutions

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

4. Graph

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