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Solution - Absolute value equations

Exact form:

x = \frac{3}{2}, - \frac{1}{8}

x=\frac{3}{2} , -\frac{1}{8}

Mixed number form:

x = 1 \frac{1}{2}, - \frac{1}{8}

x=1\frac{1}{2} , -\frac{1}{8}

Decimal form:

x = 1.5, - 0.125

x=1.5 , -0.125

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
$| x + 5 | = | 7 x - 4 |$
without the absolute value bars:

$\| x \| = \| y \|$	$\| x + 5 \| = \| 7 x - 4 \|$
$x = + y$	$(x + 5) = (7 x - 4)$
$x = - y$	$(x + 5) = - (7 x - 4)$
$+ x = y$	$(x + 5) = (7 x - 4)$
$- x = y$	$- (x + 5) = (7 x - 4)$

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:

$\| x \| = \| y \|$	$\| x + 5 \| = \| 7 x - 4 \|$
$x = + y$ , $+ x = y$	$(x + 5) = (7 x - 4)$
$x = - y$ , $- x = y$	$(x + 5) = - (7 x - 4)$

2. Solve the two equations for x

13 additional steps

$(x + 5) = (7 x - 4)$

Subtract from both sides:

$(x + 5) - 7 x = (7 x - 4) - 7 x$

Group like terms:

$(x - 7 x) + 5 = (7 x - 4) - 7 x$

Simplify the arithmetic:

$- 6 x + 5 = (7 x - 4) - 7 x$

Group like terms:

$- 6 x + 5 = (7 x - 7 x) - 4$

Simplify the arithmetic:

$- 6 x + 5 = - 4$

Subtract from both sides:

$(- 6 x + 5) - 5 = - 4 - 5$

Simplify the arithmetic:

$- 6 x = - 4 - 5$

Simplify the arithmetic:

$- 6 x = - 9$

Divide both sides by :

$\frac{(- 6 x)}{- 6} = \frac{- 9}{- 6}$

Cancel out the negatives:

$\frac{6 x}{6} = \frac{- 9}{- 6}$

Simplify the fraction:

$x = \frac{- 9}{- 6}$

Cancel out the negatives:

$x = \frac{9}{6}$

Find the greatest common factor of the numerator and denominator:

$x = \frac{(3 \cdot 3)}{(2 \cdot 3)}$

Factor out and cancel the greatest common factor:

$x = \frac{3}{2}$

10 additional steps

$(x + 5) = - (7 x - 4)$

Expand the parentheses:

$(x + 5) = - 7 x + 4$

Add to both sides:

$(x + 5) + 7 x = (- 7 x + 4) + 7 x$

Group like terms:

$(x + 7 x) + 5 = (- 7 x + 4) + 7 x$

Simplify the arithmetic:

$8 x + 5 = (- 7 x + 4) + 7 x$

Group like terms:

$8 x + 5 = (- 7 x + 7 x) + 4$

Simplify the arithmetic:

$8 x + 5 = 4$

Subtract from both sides:

$(8 x + 5) - 5 = 4 - 5$

Simplify the arithmetic:

$8 x = 4 - 5$

Simplify the arithmetic:

$8 x = - 1$

Divide both sides by :

$\frac{(8 x)}{8} = \frac{- 1}{8}$

Simplify the fraction:

$x = \frac{- 1}{8}$

3. List the solutions

$x = \frac{3}{2}, - \frac{1}{8}$
(2 solution(s))

4. Graph

Each line represents the function of one side of the equation:
$y = | x + 5 |$
$y = | 7 x - 4 |$
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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