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Solution - Absolute value equations

Exact form:

x = \frac{19}{5}, \frac{17}{13}

x=\frac{19}{5} , \frac{17}{13}

Mixed number form:

x = 3 \frac{4}{5}, 1 \frac{4}{13}

x=3\frac{4}{5} , 1\frac{4}{13}

Decimal form:

x = 3.8, 1.308

x=3.8 , 1.308

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
$| 9 x - 18 | = | 4 x + 1 |$
without the absolute value bars:

$\| x \| = \| y \|$	$\| 9 x - 18 \| = \| 4 x + 1 \|$
$x = + y$	$(9 x - 18) = (4 x + 1)$
$x = - y$	$(9 x - 18) = - (4 x + 1)$
$+ x = y$	$(9 x - 18) = (4 x + 1)$
$- x = y$	$- (9 x - 18) = (4 x + 1)$

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:

$\| x \| = \| y \|$	$\| 9 x - 18 \| = \| 4 x + 1 \|$
$x = + y$ , $+ x = y$	$(9 x - 18) = (4 x + 1)$
$x = - y$ , $- x = y$	$(9 x - 18) = - (4 x + 1)$

2. Solve the two equations for x

9 additional steps

$(9 x - 18) = (4 x + 1)$

Subtract from both sides:

$(9 x - 18) - 4 x = (4 x + 1) - 4 x$

Group like terms:

$(9 x - 4 x) - 18 = (4 x + 1) - 4 x$

Simplify the arithmetic:

$5 x - 18 = (4 x + 1) - 4 x$

Group like terms:

$5 x - 18 = (4 x - 4 x) + 1$

Simplify the arithmetic:

$5 x - 18 = 1$

Add to both sides:

$(5 x - 18) + 18 = 1 + 18$

Simplify the arithmetic:

$5 x = 1 + 18$

Simplify the arithmetic:

$5 x = 19$

Divide both sides by :

$\frac{(5 x)}{5} = \frac{19}{5}$

Simplify the fraction:

$x = \frac{19}{5}$

10 additional steps

$(9 x - 18) = - (4 x + 1)$

Expand the parentheses:

$(9 x - 18) = - 4 x - 1$

Add to both sides:

$(9 x - 18) + 4 x = (- 4 x - 1) + 4 x$

Group like terms:

$(9 x + 4 x) - 18 = (- 4 x - 1) + 4 x$

Simplify the arithmetic:

$13 x - 18 = (- 4 x - 1) + 4 x$

Group like terms:

$13 x - 18 = (- 4 x + 4 x) - 1$

Simplify the arithmetic:

$13 x - 18 = - 1$

Add to both sides:

$(13 x - 18) + 18 = - 1 + 18$

Simplify the arithmetic:

$13 x = - 1 + 18$

Simplify the arithmetic:

$13 x = 17$

Divide both sides by :

$\frac{(13 x)}{13} = \frac{17}{13}$

Simplify the fraction:

$x = \frac{17}{13}$

3. List the solutions

$x = \frac{19}{5}, \frac{17}{13}$
(2 solution(s))

4. Graph

Each line represents the function of one side of the equation:
$y = | 9 x - 18 |$
$y = | 4 x + 1 |$
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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