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Solution - Absolute value equations

Exact form:

x = \frac{7}{8}, - \frac{1}{10}

x=\frac{7}{8} , -\frac{1}{10}

Decimal form:

x = 0.875, - 0.1

x=0.875 , -0.1

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
$| x + 4 | = 3 | 3 x - 1 |$
without the absolute value bars:

$\| x \| = \| y \|$	$\| x + 4 \| = 3 \| 3 x - 1 \|$
$x = + y$	$(x + 4) = 3 (3 x - 1)$
$x = - y$	$(x + 4) = 3 (- (3 x - 1))$
$+ x = y$	$(x + 4) = 3 (3 x - 1)$
$- x = y$	$- (x + 4) = 3 (3 x - 1)$

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:

$\| x \| = \| y \|$	$\| x + 4 \| = 3 \| 3 x - 1 \|$
$x = + y$ , $+ x = y$	$(x + 4) = 3 (3 x - 1)$
$x = - y$ , $- x = y$	$(x + 4) = 3 (- (3 x - 1))$

2. Solve the two equations for x

14 additional steps

$(x + 4) = 3 \cdot (3 x - 1)$

Expand the parentheses:

$(x + 4) = 3 \cdot 3 x + 3 \cdot - 1$

Multiply the coefficients:

$(x + 4) = 9 x + 3 \cdot - 1$

Simplify the arithmetic:

$(x + 4) = 9 x - 3$

Subtract from both sides:

$(x + 4) - 9 x = (9 x - 3) - 9 x$

Group like terms:

$(x - 9 x) + 4 = (9 x - 3) - 9 x$

Simplify the arithmetic:

$- 8 x + 4 = (9 x - 3) - 9 x$

Group like terms:

$- 8 x + 4 = (9 x - 9 x) - 3$

Simplify the arithmetic:

$- 8 x + 4 = - 3$

Subtract from both sides:

$(- 8 x + 4) - 4 = - 3 - 4$

Simplify the arithmetic:

$- 8 x = - 3 - 4$

Simplify the arithmetic:

$- 8 x = - 7$

Divide both sides by :

$\frac{(- 8 x)}{- 8} = \frac{- 7}{- 8}$

Cancel out the negatives:

$\frac{8 x}{8} = \frac{- 7}{- 8}$

Simplify the fraction:

$x = \frac{- 7}{- 8}$

Cancel out the negatives:

$x = \frac{7}{8}$

13 additional steps

$(x + 4) = 3 \cdot (- (3 x - 1))$

Expand the parentheses:

$(x + 4) = 3 \cdot (- 3 x + 1)$

Expand the parentheses:

$(x + 4) = 3 \cdot - 3 x + 3 \cdot 1$

Multiply the coefficients:

$(x + 4) = - 9 x + 3 \cdot 1$

Simplify the arithmetic:

$(x + 4) = - 9 x + 3$

Add to both sides:

$(x + 4) + 9 x = (- 9 x + 3) + 9 x$

Group like terms:

$(x + 9 x) + 4 = (- 9 x + 3) + 9 x$

Simplify the arithmetic:

$10 x + 4 = (- 9 x + 3) + 9 x$

Group like terms:

$10 x + 4 = (- 9 x + 9 x) + 3$

Simplify the arithmetic:

$10 x + 4 = 3$

Subtract from both sides:

$(10 x + 4) - 4 = 3 - 4$

Simplify the arithmetic:

$10 x = 3 - 4$

Simplify the arithmetic:

$10 x = - 1$

Divide both sides by :

$\frac{(10 x)}{10} = \frac{- 1}{10}$

Simplify the fraction:

$x = \frac{- 1}{10}$

3. List the solutions

$x = \frac{7}{8}, - \frac{1}{10}$
(2 solution(s))

4. Graph

Each line represents the function of one side of the equation:
$y = | x + 4 |$
$y = 3 | 3 x - 1 |$
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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