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Solution - Absolute value equations

Exact form:

x = - 3, 15

x=-3 , 15

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
$| - 3 x | = | 2 x + 15 |$
without the absolute value bars:

$\| x \| = \| y \|$	$\| - 3 x \| = \| 2 x + 15 \|$
$x = + y$	$(- 3 x) = (2 x + 15)$
$x = - y$	$(- 3 x) = - (2 x + 15)$
$+ x = y$	$(- 3 x) = (2 x + 15)$
$- x = y$	$- (- 3 x) = (2 x + 15)$

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:

$\| x \| = \| y \|$	$\| - 3 x \| = \| 2 x + 15 \|$
$x = + y$ , $+ x = y$	$(- 3 x) = (2 x + 15)$
$x = - y$ , $- x = y$	$(- 3 x) = - (2 x + 15)$

2. Solve the two equations for x

9 additional steps

$(- 3 x) = (2 x + 15)$

Subtract from both sides:

$(- 3 x) - 2 x = (2 x + 15) - 2 x$

Simplify the arithmetic:

$- 5 x = (2 x + 15) - 2 x$

Group like terms:

$- 5 x = (2 x - 2 x) + 15$

Simplify the arithmetic:

$- 5 x = 15$

Divide both sides by :

$\frac{(- 5 x)}{- 5} = \frac{15}{- 5}$

Cancel out the negatives:

$\frac{5 x}{5} = \frac{15}{- 5}$

Simplify the fraction:

$x = \frac{15}{- 5}$

Move the negative sign from the denominator to the numerator:

$x = \frac{- 15}{5}$

Find the greatest common factor of the numerator and denominator:

$x = \frac{(- 3 \cdot 5)}{(1 \cdot 5)}$

Factor out and cancel the greatest common factor:

$x = - 3$

7 additional steps

$(- 3 x) = - (2 x + 15)$

Expand the parentheses:

$(- 3 x) = - 2 x - 15$

Add to both sides:

$(- 3 x) + 2 x = (- 2 x - 15) + 2 x$

Simplify the arithmetic:

$- x = (- 2 x - 15) + 2 x$

Group like terms:

$- x = (- 2 x + 2 x) - 15$

Simplify the arithmetic:

$- x = - 15$

Multiply both sides by :

$- x \cdot - 1 = - 15 \cdot - 1$

Remove the one(s):

$x = - 15 \cdot - 1$

Simplify the arithmetic:

$x = 15$

3. List the solutions

$x = - 3, 15$
(2 solution(s))

4. Graph

Each line represents the function of one side of the equation:
$y = | - 3 x |$
$y = | 2 x + 15 |$
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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