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Solution - Absolute value equations

Exact form:

x = \frac{2}{3}, - 8

x=\frac{2}{3} , -8

Decimal form:

x = 0.667, - 8

x=0.667 , -8

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
$| - 5 x - 1 | = | 4 x - 7 |$
without the absolute value bars:

$\| x \| = \| y \|$	$\| - 5 x - 1 \| = \| 4 x - 7 \|$
$x = + y$	$(- 5 x - 1) = (4 x - 7)$
$x = - y$	$(- 5 x - 1) = - (4 x - 7)$
$+ x = y$	$(- 5 x - 1) = (4 x - 7)$
$- x = y$	$- (- 5 x - 1) = (4 x - 7)$

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:

$\| x \| = \| y \|$	$\| - 5 x - 1 \| = \| 4 x - 7 \|$
$x = + y$ , $+ x = y$	$(- 5 x - 1) = (4 x - 7)$
$x = - y$ , $- x = y$	$(- 5 x - 1) = - (4 x - 7)$

2. Solve the two equations for x

13 additional steps

$(- 5 x - 1) = (4 x - 7)$

Subtract from both sides:

$(- 5 x - 1) - 4 x = (4 x - 7) - 4 x$

Group like terms:

$(- 5 x - 4 x) - 1 = (4 x - 7) - 4 x$

Simplify the arithmetic:

$- 9 x - 1 = (4 x - 7) - 4 x$

Group like terms:

$- 9 x - 1 = (4 x - 4 x) - 7$

Simplify the arithmetic:

$- 9 x - 1 = - 7$

Add to both sides:

$(- 9 x - 1) + 1 = - 7 + 1$

Simplify the arithmetic:

$- 9 x = - 7 + 1$

Simplify the arithmetic:

$- 9 x = - 6$

Divide both sides by :

$\frac{(- 9 x)}{- 9} = \frac{- 6}{- 9}$

Cancel out the negatives:

$\frac{9 x}{9} = \frac{- 6}{- 9}$

Simplify the fraction:

$x = \frac{- 6}{- 9}$

Cancel out the negatives:

$x = \frac{6}{9}$

Find the greatest common factor of the numerator and denominator:

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

Factor out and cancel the greatest common factor:

$x = \frac{2}{3}$

11 additional steps

$(- 5 x - 1) = - (4 x - 7)$

Expand the parentheses:

$(- 5 x - 1) = - 4 x + 7$

Add to both sides:

$(- 5 x - 1) + 4 x = (- 4 x + 7) + 4 x$

Group like terms:

$(- 5 x + 4 x) - 1 = (- 4 x + 7) + 4 x$

Simplify the arithmetic:

$- x - 1 = (- 4 x + 7) + 4 x$

Group like terms:

$- x - 1 = (- 4 x + 4 x) + 7$

Simplify the arithmetic:

$- x - 1 = 7$

Add to both sides:

$(- x - 1) + 1 = 7 + 1$

Simplify the arithmetic:

$- x = 7 + 1$

Simplify the arithmetic:

$- x = 8$

Multiply both sides by :

$- x \cdot - 1 = 8 \cdot - 1$

Remove the one(s):

$x = 8 \cdot - 1$

Simplify the arithmetic:

$x = - 8$

3. List the solutions

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

4. Graph

Each line represents the function of one side of the equation:
$y = | - 5 x - 1 |$
$y = | 4 x - 7 |$
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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