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Solution - Absolute value equations

Exact form:

x = - \frac{5}{11}, \frac{9}{5}

x=-\frac{5}{11} , \frac{9}{5}

Mixed number form:

x = - \frac{5}{11}, 1 \frac{4}{5}

x=-\frac{5}{11} , 1\frac{4}{5}

Decimal form:

x = - 0.455, 1.8

x=-0.455 , 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
$| 3 x + 7 | = - | 8 x - 2 |$
without the absolute value bars:

$\| x \| = \| y \|$	$\| 3 x + 7 \| = - \| 8 x - 2 \|$
$x = + y$	$(3 x + 7) = - (8 x - 2)$
$x = - y$	$(3 x + 7) = - (- (8 x - 2))$
$+ x = y$	$(3 x + 7) = - (8 x - 2)$
$- x = y$	$- (3 x + 7) = - (8 x - 2)$

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:

$\| x \| = \| y \|$	$\| 3 x + 7 \| = - \| 8 x - 2 \|$
$x = + y$ , $+ x = y$	$(3 x + 7) = - (8 x - 2)$
$x = - y$ , $- x = y$	$(3 x + 7) = - (- (8 x - 2))$

2. Solve the two equations for x

10 additional steps

$(3 x + 7) = - (8 x - 2)$

Expand the parentheses:

$(3 x + 7) = - 8 x + 2$

Add to both sides:

$(3 x + 7) + 8 x = (- 8 x + 2) + 8 x$

Group like terms:

$(3 x + 8 x) + 7 = (- 8 x + 2) + 8 x$

Simplify the arithmetic:

$11 x + 7 = (- 8 x + 2) + 8 x$

Group like terms:

$11 x + 7 = (- 8 x + 8 x) + 2$

Simplify the arithmetic:

$11 x + 7 = 2$

Subtract from both sides:

$(11 x + 7) - 7 = 2 - 7$

Simplify the arithmetic:

$11 x = 2 - 7$

Simplify the arithmetic:

$11 x = - 5$

Divide both sides by :

$\frac{(11 x)}{11} = \frac{- 5}{11}$

Simplify the fraction:

$x = \frac{- 5}{11}$

12 additional steps

$(3 x + 7) = - (- (8 x - 2))$

NT_MSLUS_MAINSTEP_RESOLVE_DOUBLE_MINUS:

$(3 x + 7) = 8 x - 2$

Subtract from both sides:

$(3 x + 7) - 8 x = (8 x - 2) - 8 x$

Group like terms:

$(3 x - 8 x) + 7 = (8 x - 2) - 8 x$

Simplify the arithmetic:

$- 5 x + 7 = (8 x - 2) - 8 x$

Group like terms:

$- 5 x + 7 = (8 x - 8 x) - 2$

Simplify the arithmetic:

$- 5 x + 7 = - 2$

Subtract from both sides:

$(- 5 x + 7) - 7 = - 2 - 7$

Simplify the arithmetic:

$- 5 x = - 2 - 7$

Simplify the arithmetic:

$- 5 x = - 9$

Divide both sides by :

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

Cancel out the negatives:

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

Simplify the fraction:

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

Cancel out the negatives:

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

3. List the solutions

$x = - \frac{5}{11}, \frac{9}{5}$
(2 solution(s))

4. Graph

Each line represents the function of one side of the equation:
$y = | 3 x + 7 |$
$y = - | 8 x - 2 |$
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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