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Solution - Absolute value equations

Exact form:

x = - \frac{14}{3}, - \frac{16}{7}

x=-\frac{14}{3} , -\frac{16}{7}

Mixed number form:

x = - 4 \frac{2}{3}, - 2 \frac{2}{7}

x=-4\frac{2}{3} , -2\frac{2}{7}

Decimal form:

x = - 4.667, - 2.286

x=-4.667 , -2.286

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
$| 2 x + 1 | = | 5 x + 15 |$
without the absolute value bars:

$\| x \| = \| y \|$	$\| 2 x + 1 \| = \| 5 x + 15 \|$
$x = + y$	$(2 x + 1) = (5 x + 15)$
$x = - y$	$(2 x + 1) = - (5 x + 15)$
$+ x = y$	$(2 x + 1) = (5 x + 15)$
$- x = y$	$- (2 x + 1) = (5 x + 15)$

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:

$\| x \| = \| y \|$	$\| 2 x + 1 \| = \| 5 x + 15 \|$
$x = + y$ , $+ x = y$	$(2 x + 1) = (5 x + 15)$
$x = - y$ , $- x = y$	$(2 x + 1) = - (5 x + 15)$

2. Solve the two equations for x

11 additional steps

$(2 x + 1) = (5 x + 15)$

Subtract from both sides:

$(2 x + 1) - 5 x = (5 x + 15) - 5 x$

Group like terms:

$(2 x - 5 x) + 1 = (5 x + 15) - 5 x$

Simplify the arithmetic:

$- 3 x + 1 = (5 x + 15) - 5 x$

Group like terms:

$- 3 x + 1 = (5 x - 5 x) + 15$

Simplify the arithmetic:

$- 3 x + 1 = 15$

Subtract from both sides:

$(- 3 x + 1) - 1 = 15 - 1$

Simplify the arithmetic:

$- 3 x = 15 - 1$

Simplify the arithmetic:

$- 3 x = 14$

Divide both sides by :

$\frac{(- 3 x)}{- 3} = \frac{14}{- 3}$

Cancel out the negatives:

$\frac{3 x}{3} = \frac{14}{- 3}$

Simplify the fraction:

$x = \frac{14}{- 3}$

Move the negative sign from the denominator to the numerator:

$x = \frac{- 14}{3}$

10 additional steps

$(2 x + 1) = - (5 x + 15)$

Expand the parentheses:

$(2 x + 1) = - 5 x - 15$

Add to both sides:

$(2 x + 1) + 5 x = (- 5 x - 15) + 5 x$

Group like terms:

$(2 x + 5 x) + 1 = (- 5 x - 15) + 5 x$

Simplify the arithmetic:

$7 x + 1 = (- 5 x - 15) + 5 x$

Group like terms:

$7 x + 1 = (- 5 x + 5 x) - 15$

Simplify the arithmetic:

$7 x + 1 = - 15$

Subtract from both sides:

$(7 x + 1) - 1 = - 15 - 1$

Simplify the arithmetic:

$7 x = - 15 - 1$

Simplify the arithmetic:

$7 x = - 16$

Divide both sides by :

$\frac{(7 x)}{7} = \frac{- 16}{7}$

Simplify the fraction:

$x = \frac{- 16}{7}$

3. List the solutions

$x = - \frac{14}{3}, - \frac{16}{7}$
(2 solution(s))

4. Graph

Each line represents the function of one side of the equation:
$y = | 2 x + 1 |$
$y = | 5 x + 15 |$
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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