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Solution - Absolute value equations

Exact form:

x = - \frac{3}{2}

x=-\frac{3}{2}

Mixed number form:

x = - 1 \frac{1}{2}

x=-1\frac{1}{2}

Decimal form:

x = - 1.5

x=-1.5

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
$| - 3 x - 5 | = | 3 x + 4 |$
without the absolute value bars:

$\| x \| = \| y \|$	$\| - 3 x - 5 \| = \| 3 x + 4 \|$
$x = + y$	$(- 3 x - 5) = (3 x + 4)$
$x = - y$	$(- 3 x - 5) = - (3 x + 4)$
$+ x = y$	$(- 3 x - 5) = (3 x + 4)$
$- x = y$	$- (- 3 x - 5) = (3 x + 4)$

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:

$\| x \| = \| y \|$	$\| - 3 x - 5 \| = \| 3 x + 4 \|$
$x = + y$ , $+ x = y$	$(- 3 x - 5) = (3 x + 4)$
$x = - y$ , $- x = y$	$(- 3 x - 5) = - (3 x + 4)$

2. Solve the two equations for x

13 additional steps

$(- 3 x - 5) = (3 x + 4)$

Subtract from both sides:

$(- 3 x - 5) - 3 x = (3 x + 4) - 3 x$

Group like terms:

$(- 3 x - 3 x) - 5 = (3 x + 4) - 3 x$

Simplify the arithmetic:

$- 6 x - 5 = (3 x + 4) - 3 x$

Group like terms:

$- 6 x - 5 = (3 x - 3 x) + 4$

Simplify the arithmetic:

$- 6 x - 5 = 4$

Add to both sides:

$(- 6 x - 5) + 5 = 4 + 5$

Simplify the arithmetic:

$- 6 x = 4 + 5$

Simplify the arithmetic:

$- 6 x = 9$

Divide both sides by :

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

Cancel out the negatives:

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

Simplify the fraction:

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

Move the negative sign from the denominator to the numerator:

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

Find the greatest common factor of the numerator and denominator:

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

Factor out and cancel the greatest common factor:

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

6 additional steps

$(- 3 x - 5) = - (3 x + 4)$

Expand the parentheses:

$(- 3 x - 5) = - 3 x - 4$

Add to both sides:

$(- 3 x - 5) + 3 x = (- 3 x - 4) + 3 x$

Group like terms:

$(- 3 x + 3 x) - 5 = (- 3 x - 4) + 3 x$

Simplify the arithmetic:

$- 5 = (- 3 x - 4) + 3 x$

Group like terms:

$- 5 = (- 3 x + 3 x) - 4$

Simplify the arithmetic:

$- 5 = - 4$

The statement is false:

$- 5 = - 4$

The equation is false so it has no solution.

3. List the solutions

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

4. Graph

Each line represents the function of one side of the equation:
$y = | - 3 x - 5 |$
$y = | 3 x + 4 |$
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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