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Solution - Absolute value equations

Exact form:

x = \frac{11}{3}, 19

x=\frac{11}{3} , 19

Mixed number form:

x = 3 \frac{2}{3}, 19

x=3\frac{2}{3} , 19

Decimal form:

x = 3.667, 19

x=3.667 , 19

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
$| - 2 x + 15 | = | x + 4 |$
without the absolute value bars:

$\| x \| = \| y \|$	$\| - 2 x + 15 \| = \| x + 4 \|$
$x = + y$	$(- 2 x + 15) = (x + 4)$
$x = - y$	$(- 2 x + 15) = - (x + 4)$
$+ x = y$	$(- 2 x + 15) = (x + 4)$
$- x = y$	$- (- 2 x + 15) = (x + 4)$

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:

$\| x \| = \| y \|$	$\| - 2 x + 15 \| = \| x + 4 \|$
$x = + y$ , $+ x = y$	$(- 2 x + 15) = (x + 4)$
$x = - y$ , $- x = y$	$(- 2 x + 15) = - (x + 4)$

2. Solve the two equations for x

11 additional steps

$(- 2 x + 15) = (x + 4)$

Subtract from both sides:

$(- 2 x + 15) - x = (x + 4) - x$

Group like terms:

$(- 2 x - x) + 15 = (x + 4) - x$

Simplify the arithmetic:

$- 3 x + 15 = (x + 4) - x$

Group like terms:

$- 3 x + 15 = (x - x) + 4$

Simplify the arithmetic:

$- 3 x + 15 = 4$

Subtract from both sides:

$(- 3 x + 15) - 15 = 4 - 15$

Simplify the arithmetic:

$- 3 x = 4 - 15$

Simplify the arithmetic:

$- 3 x = - 11$

Divide both sides by :

$\frac{(- 3 x)}{- 3} = \frac{- 11}{- 3}$

Cancel out the negatives:

$\frac{3 x}{3} = \frac{- 11}{- 3}$

Simplify the fraction:

$x = \frac{- 11}{- 3}$

Cancel out the negatives:

$x = \frac{11}{3}$

11 additional steps

$(- 2 x + 15) = - (x + 4)$

Expand the parentheses:

$(- 2 x + 15) = - x - 4$

Add to both sides:

$(- 2 x + 15) + x = (- x - 4) + x$

Group like terms:

$(- 2 x + x) + 15 = (- x - 4) + x$

Simplify the arithmetic:

$- x + 15 = (- x - 4) + x$

Group like terms:

$- x + 15 = (- x + x) - 4$

Simplify the arithmetic:

$- x + 15 = - 4$

Subtract from both sides:

$(- x + 15) - 15 = - 4 - 15$

Simplify the arithmetic:

$- x = - 4 - 15$

Simplify the arithmetic:

$- x = - 19$

Multiply both sides by :

$- x \cdot - 1 = - 19 \cdot - 1$

Remove the one(s):

$x = - 19 \cdot - 1$

Simplify the arithmetic:

$x = 19$

3. List the solutions

$x = \frac{11}{3}, 19$
(2 solution(s))

4. Graph

Each line represents the function of one side of the equation:
$y = | - 2 x + 15 |$
$y = | x + 4 |$
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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