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Solution - Absolute value equations

Exact form:

x = - \frac{1}{3}, - \frac{9}{5}

x=-\frac{1}{3} , -\frac{9}{5}

Mixed number form:

x = - \frac{1}{3}, - 1 \frac{4}{5}

x=-\frac{1}{3} , -1\frac{4}{5}

Decimal form:

x = - 0.333, - 1.8

x=-0.333 , -1.8

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
$| 4 x + 5 | = | x + 4 |$
without the absolute value bars:

$\| x \| = \| y \|$	$\| 4 x + 5 \| = \| x + 4 \|$
$x = + y$	$(4 x + 5) = (x + 4)$
$x = - y$	$(4 x + 5) = - (x + 4)$
$+ x = y$	$(4 x + 5) = (x + 4)$
$- x = y$	$- (4 x + 5) = (x + 4)$

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:

$\| x \| = \| y \|$	$\| 4 x + 5 \| = \| x + 4 \|$
$x = + y$ , $+ x = y$	$(4 x + 5) = (x + 4)$
$x = - y$ , $- x = y$	$(4 x + 5) = - (x + 4)$

2. Solve the two equations for x

9 additional steps

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

Subtract from both sides:

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

Group like terms:

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

Simplify the arithmetic:

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

Group like terms:

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

Simplify the arithmetic:

$3 x + 5 = 4$

Subtract from both sides:

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

Simplify the arithmetic:

$3 x = 4 - 5$

Simplify the arithmetic:

$3 x = - 1$

Divide both sides by :

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

Simplify the fraction:

$x = \frac{- 1}{3}$

10 additional steps

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

Expand the parentheses:

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

Add to both sides:

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

Group like terms:

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

Simplify the arithmetic:

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

Group like terms:

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

Simplify the arithmetic:

$5 x + 5 = - 4$

Subtract from both sides:

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

Simplify the arithmetic:

$5 x = - 4 - 5$

Simplify the arithmetic:

$5 x = - 9$

Divide both sides by :

$\frac{(5 x)}{5} = \frac{- 9}{5}$

Simplify the fraction:

$x = \frac{- 9}{5}$

3. List the solutions

$x = - \frac{1}{3}, - \frac{9}{5}$
(2 solution(s))

4. Graph

Each line represents the function of one side of the equation:
$y = | 4 x + 5 |$
$y = | x + 4 |$
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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