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Solution - Absolute value equations

Exact form:

x = \frac{8}{3}, - 4

x=\frac{8}{3} , -4

Mixed number form:

x = 2 \frac{2}{3}, - 4

x=2\frac{2}{3} , -4

Decimal form:

x = 2.667, - 4

x=2.667 , -4

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
$| 5 x - 20 | = | - 7 x + 12 |$
without the absolute value bars:

$\| x \| = \| y \|$	$\| 5 x - 20 \| = \| - 7 x + 12 \|$
$x = + y$	$(5 x - 20) = (- 7 x + 12)$
$x = - y$	$(5 x - 20) = - (- 7 x + 12)$
$+ x = y$	$(5 x - 20) = (- 7 x + 12)$
$- x = y$	$- (5 x - 20) = (- 7 x + 12)$

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:

$\| x \| = \| y \|$	$\| 5 x - 20 \| = \| - 7 x + 12 \|$
$x = + y$ , $+ x = y$	$(5 x - 20) = (- 7 x + 12)$
$x = - y$ , $- x = y$	$(5 x - 20) = - (- 7 x + 12)$

2. Solve the two equations for x

11 additional steps

$(5 x - 20) = (- 7 x + 12)$

Add to both sides:

$(5 x - 20) + 7 x = (- 7 x + 12) + 7 x$

Group like terms:

$(5 x + 7 x) - 20 = (- 7 x + 12) + 7 x$

Simplify the arithmetic:

$12 x - 20 = (- 7 x + 12) + 7 x$

Group like terms:

$12 x - 20 = (- 7 x + 7 x) + 12$

Simplify the arithmetic:

$12 x - 20 = 12$

Add to both sides:

$(12 x - 20) + 20 = 12 + 20$

Simplify the arithmetic:

$12 x = 12 + 20$

Simplify the arithmetic:

$12 x = 32$

Divide both sides by :

$\frac{(12 x)}{12} = \frac{32}{12}$

Simplify the fraction:

$x = \frac{32}{12}$

Find the greatest common factor of the numerator and denominator:

$x = \frac{(8 \cdot 4)}{(3 \cdot 4)}$

Factor out and cancel the greatest common factor:

$x = \frac{8}{3}$

14 additional steps

$(5 x - 20) = - (- 7 x + 12)$

Expand the parentheses:

$(5 x - 20) = 7 x - 12$

Subtract from both sides:

$(5 x - 20) - 7 x = (7 x - 12) - 7 x$

Group like terms:

$(5 x - 7 x) - 20 = (7 x - 12) - 7 x$

Simplify the arithmetic:

$- 2 x - 20 = (7 x - 12) - 7 x$

Group like terms:

$- 2 x - 20 = (7 x - 7 x) - 12$

Simplify the arithmetic:

$- 2 x - 20 = - 12$

Add to both sides:

$(- 2 x - 20) + 20 = - 12 + 20$

Simplify the arithmetic:

$- 2 x = - 12 + 20$

Simplify the arithmetic:

$- 2 x = 8$

Divide both sides by :

$\frac{(- 2 x)}{- 2} = \frac{8}{- 2}$

Cancel out the negatives:

$\frac{2 x}{2} = \frac{8}{- 2}$

Simplify the fraction:

$x = \frac{8}{- 2}$

Move the negative sign from the denominator to the numerator:

$x = \frac{- 8}{2}$

Find the greatest common factor of the numerator and denominator:

$x = \frac{(- 4 \cdot 2)}{(1 \cdot 2)}$

Factor out and cancel the greatest common factor:

$x = - 4$

3. List the solutions

$x = \frac{8}{3}, - 4$
(2 solution(s))

4. Graph

Each line represents the function of one side of the equation:
$y = | 5 x - 20 |$
$y = | - 7 x + 12 |$
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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