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Solution - Absolute value equations

Exact form:

x = \frac{7}{5}, 9

x=\frac{7}{5} , 9

Mixed number form:

x = 1 \frac{2}{5}, 9

x=1\frac{2}{5} , 9

Decimal form:

x = 1.4, 9

x=1.4 , 9

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
$| - 3 x + 8 | = | 2 x + 1 |$
without the absolute value bars:

$\| x \| = \| y \|$	$\| - 3 x + 8 \| = \| 2 x + 1 \|$
$x = + y$	$(- 3 x + 8) = (2 x + 1)$
$x = - y$	$(- 3 x + 8) = - (2 x + 1)$
$+ x = y$	$(- 3 x + 8) = (2 x + 1)$
$- x = y$	$- (- 3 x + 8) = (2 x + 1)$

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:

$\| x \| = \| y \|$	$\| - 3 x + 8 \| = \| 2 x + 1 \|$
$x = + y$ , $+ x = y$	$(- 3 x + 8) = (2 x + 1)$
$x = - y$ , $- x = y$	$(- 3 x + 8) = - (2 x + 1)$

2. Solve the two equations for x

11 additional steps

$(- 3 x + 8) = (2 x + 1)$

Subtract from both sides:

$(- 3 x + 8) - 2 x = (2 x + 1) - 2 x$

Group like terms:

$(- 3 x - 2 x) + 8 = (2 x + 1) - 2 x$

Simplify the arithmetic:

$- 5 x + 8 = (2 x + 1) - 2 x$

Group like terms:

$- 5 x + 8 = (2 x - 2 x) + 1$

Simplify the arithmetic:

$- 5 x + 8 = 1$

Subtract from both sides:

$(- 5 x + 8) - 8 = 1 - 8$

Simplify the arithmetic:

$- 5 x = 1 - 8$

Simplify the arithmetic:

$- 5 x = - 7$

Divide both sides by :

$\frac{(- 5 x)}{- 5} = \frac{- 7}{- 5}$

Cancel out the negatives:

$\frac{5 x}{5} = \frac{- 7}{- 5}$

Simplify the fraction:

$x = \frac{- 7}{- 5}$

Cancel out the negatives:

$x = \frac{7}{5}$

11 additional steps

$(- 3 x + 8) = - (2 x + 1)$

Expand the parentheses:

$(- 3 x + 8) = - 2 x - 1$

Add to both sides:

$(- 3 x + 8) + 2 x = (- 2 x - 1) + 2 x$

Group like terms:

$(- 3 x + 2 x) + 8 = (- 2 x - 1) + 2 x$

Simplify the arithmetic:

$- x + 8 = (- 2 x - 1) + 2 x$

Group like terms:

$- x + 8 = (- 2 x + 2 x) - 1$

Simplify the arithmetic:

$- x + 8 = - 1$

Subtract from both sides:

$(- x + 8) - 8 = - 1 - 8$

Simplify the arithmetic:

$- x = - 1 - 8$

Simplify the arithmetic:

$- x = - 9$

Multiply both sides by :

$- x \cdot - 1 = - 9 \cdot - 1$

Remove the one(s):

$x = - 9 \cdot - 1$

Simplify the arithmetic:

$x = 9$

3. List the solutions

$x = \frac{7}{5}, 9$
(2 solution(s))

4. Graph

Each line represents the function of one side of the equation:
$y = | - 3 x + 8 |$
$y = | 2 x + 1 |$
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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