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Solution - Absolute value equations

Exact form:

x = - \frac{12}{7}, - \frac{4}{5}

x=-\frac{12}{7} , -\frac{4}{5}

Mixed number form:

x = - 1 \frac{5}{7}, - \frac{4}{5}

x=-1\frac{5}{7} , -\frac{4}{5}

Decimal form:

x = - 1.714, - 0.8

x=-1.714 , -0.8

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
$| 4 x | = | 11 x + 12 |$
without the absolute value bars:

$\| x \| = \| y \|$	$\| 4 x \| = \| 11 x + 12 \|$
$x = + y$	$(4 x) = (11 x + 12)$
$x = - y$	$(4 x) = - (11 x + 12)$
$+ x = y$	$(4 x) = (11 x + 12)$
$- x = y$	$- (4 x) = (11 x + 12)$

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:

$\| x \| = \| y \|$	$\| 4 x \| = \| 11 x + 12 \|$
$x = + y$ , $+ x = y$	$(4 x) = (11 x + 12)$
$x = - y$ , $- x = y$	$(4 x) = - (11 x + 12)$

2. Solve the two equations for x

7 additional steps

$4 x = (11 x + 12)$

Subtract from both sides:

$(4 x) - 11 x = (11 x + 12) - 11 x$

Simplify the arithmetic:

$- 7 x = (11 x + 12) - 11 x$

Group like terms:

$- 7 x = (11 x - 11 x) + 12$

Simplify the arithmetic:

$- 7 x = 12$

Divide both sides by :

$\frac{(- 7 x)}{- 7} = \frac{12}{- 7}$

Cancel out the negatives:

$\frac{7 x}{7} = \frac{12}{- 7}$

Simplify the fraction:

$x = \frac{12}{- 7}$

Move the negative sign from the denominator to the numerator:

$x = \frac{- 12}{7}$

8 additional steps

$4 x = - (11 x + 12)$

Expand the parentheses:

$4 x = - 11 x - 12$

Add to both sides:

$(4 x) + 11 x = (- 11 x - 12) + 11 x$

Simplify the arithmetic:

$15 x = (- 11 x - 12) + 11 x$

Group like terms:

$15 x = (- 11 x + 11 x) - 12$

Simplify the arithmetic:

$15 x = - 12$

Divide both sides by :

$\frac{(15 x)}{15} = \frac{- 12}{15}$

Simplify the fraction:

$x = \frac{- 12}{15}$

Find the greatest common factor of the numerator and denominator:

$x = \frac{(- 4 \cdot 3)}{(5 \cdot 3)}$

Factor out and cancel the greatest common factor:

$x = \frac{- 4}{5}$

3. List the solutions

$x = - \frac{12}{7}, - \frac{4}{5}$
(2 solution(s))

4. Graph

Each line represents the function of one side of the equation:
$y = | 4 x |$
$y = | 11 x + 12 |$
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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