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Solution - Absolute value equations

Exact form:

x = \frac{21}{4}, - \frac{5}{2}

x=\frac{21}{4} , -\frac{5}{2}

Mixed number form:

x = 5 \frac{1}{4}, - 2 \frac{1}{2}

x=5\frac{1}{4} , -2\frac{1}{2}

Decimal form:

x = 5.25, - 2.5

x=5.25 , -2.5

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
$| 5 x - 3 | = | x + 18 |$
without the absolute value bars:

$\| x \| = \| y \|$	$\| 5 x - 3 \| = \| x + 18 \|$
$x = + y$	$(5 x - 3) = (x + 18)$
$x = - y$	$(5 x - 3) = - (x + 18)$
$+ x = y$	$(5 x - 3) = (x + 18)$
$- x = y$	$- (5 x - 3) = (x + 18)$

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:

$\| x \| = \| y \|$	$\| 5 x - 3 \| = \| x + 18 \|$
$x = + y$ , $+ x = y$	$(5 x - 3) = (x + 18)$
$x = - y$ , $- x = y$	$(5 x - 3) = - (x + 18)$

2. Solve the two equations for x

9 additional steps

$(5 x - 3) = (x + 18)$

Subtract from both sides:

$(5 x - 3) - x = (x + 18) - x$

Group like terms:

$(5 x - x) - 3 = (x + 18) - x$

Simplify the arithmetic:

$4 x - 3 = (x + 18) - x$

Group like terms:

$4 x - 3 = (x - x) + 18$

Simplify the arithmetic:

$4 x - 3 = 18$

Add to both sides:

$(4 x - 3) + 3 = 18 + 3$

Simplify the arithmetic:

$4 x = 18 + 3$

Simplify the arithmetic:

$4 x = 21$

Divide both sides by :

$\frac{(4 x)}{4} = \frac{21}{4}$

Simplify the fraction:

$x = \frac{21}{4}$

12 additional steps

$(5 x - 3) = - (x + 18)$

Expand the parentheses:

$(5 x - 3) = - x - 18$

Add to both sides:

$(5 x - 3) + x = (- x - 18) + x$

Group like terms:

$(5 x + x) - 3 = (- x - 18) + x$

Simplify the arithmetic:

$6 x - 3 = (- x - 18) + x$

Group like terms:

$6 x - 3 = (- x + x) - 18$

Simplify the arithmetic:

$6 x - 3 = - 18$

Add to both sides:

$(6 x - 3) + 3 = - 18 + 3$

Simplify the arithmetic:

$6 x = - 18 + 3$

Simplify the arithmetic:

$6 x = - 15$

Divide both sides by :

$\frac{(6 x)}{6} = \frac{- 15}{6}$

Simplify the fraction:

$x = \frac{- 15}{6}$

Find the greatest common factor of the numerator and denominator:

$x = \frac{(- 5 \cdot 3)}{(2 \cdot 3)}$

Factor out and cancel the greatest common factor:

$x = \frac{- 5}{2}$

3. List the solutions

$x = \frac{21}{4}, - \frac{5}{2}$
(2 solution(s))

4. Graph

Each line represents the function of one side of the equation:
$y = | 5 x - 3 |$
$y = | x + 18 |$
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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