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

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

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:

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

2. Solve the two equations for x

7 additional steps

$- x = (x + 3)$

Subtract from both sides:

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

Simplify the arithmetic:

$- 2 x = (x + 3) - x$

Group like terms:

$- 2 x = (x - x) + 3$

Simplify the arithmetic:

$- 2 x = 3$

Divide both sides by :

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

Cancel out the negatives:

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

Simplify the fraction:

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

Move the negative sign from the denominator to the numerator:

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

5 additional steps

$- x = - (x + 3)$

Expand the parentheses:

$- x = - x - 3$

Add to both sides:

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

Simplify the arithmetic:

$0 = (- x - 3) + x$

Group like terms:

$0 = (- x + x) - 3$

Simplify the arithmetic:

$0 = - 3$

The statement is false:

$0 = - 3$

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:
$y = - | x |$
$y = | x + 3 |$
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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