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Solution - Absolute value equations

Exact form:

x = - \frac{15}{2}, 5

x=-\frac{15}{2} , 5

Mixed number form:

x = - 7 \frac{1}{2}, 5

x=-7\frac{1}{2} , 5

Decimal form:

x = - 7.5, 5

x=-7.5 , 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
$| 5 x | = | x - 30 |$
without the absolute value bars:

$\| x \| = \| y \|$	$\| 5 x \| = \| x - 30 \|$
$x = + y$	$(5 x) = (x - 30)$
$x = - y$	$(5 x) = - (x - 30)$
$+ x = y$	$(5 x) = (x - 30)$
$- x = y$	$- (5 x) = (x - 30)$

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:

$\| x \| = \| y \|$	$\| 5 x \| = \| x - 30 \|$
$x = + y$ , $+ x = y$	$(5 x) = (x - 30)$
$x = - y$ , $- x = y$	$(5 x) = - (x - 30)$

2. Solve the two equations for x

7 additional steps

$5 x = (x - 30)$

Subtract from both sides:

$(5 x) - x = (x - 30) - x$

Simplify the arithmetic:

$4 x = (x - 30) - x$

Group like terms:

$4 x = (x - x) - 30$

Simplify the arithmetic:

$4 x = - 30$

Divide both sides by :

$\frac{(4 x)}{4} = \frac{- 30}{4}$

Simplify the fraction:

$x = \frac{- 30}{4}$

Find the greatest common factor of the numerator and denominator:

$x = \frac{(- 15 \cdot 2)}{(2 \cdot 2)}$

Factor out and cancel the greatest common factor:

$x = \frac{- 15}{2}$

8 additional steps

$5 x = - (x - 30)$

Expand the parentheses:

$5 x = - x + 30$

Add to both sides:

$(5 x) + x = (- x + 30) + x$

Simplify the arithmetic:

$6 x = (- x + 30) + x$

Group like terms:

$6 x = (- x + x) + 30$

Simplify the arithmetic:

$6 x = 30$

Divide both sides by :

$\frac{(6 x)}{6} = \frac{30}{6}$

Simplify the fraction:

$x = \frac{30}{6}$

Find the greatest common factor of the numerator and denominator:

$x = \frac{(5 \cdot 6)}{(1 \cdot 6)}$

Factor out and cancel the greatest common factor:

$x = 5$

3. List the solutions

$x = - \frac{15}{2}, 5$
(2 solution(s))

4. Graph

Each line represents the function of one side of the equation:
$y = | 5 x |$
$y = | x - 30 |$
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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