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Solution - Absolute value equations

Exact form:

x = - 10, \frac{8}{9}

x=-10 , \frac{8}{9}

Decimal form:

x = - 10, 0.889

x=-10 , 0.889

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
$| 5 x + 1 | = | 4 x - 9 |$
without the absolute value bars:

$\| x \| = \| y \|$	$\| 5 x + 1 \| = \| 4 x - 9 \|$
$x = + y$	$(5 x + 1) = (4 x - 9)$
$x = - y$	$(5 x + 1) = - (4 x - 9)$
$+ x = y$	$(5 x + 1) = (4 x - 9)$
$- x = y$	$- (5 x + 1) = (4 x - 9)$

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:

$\| x \| = \| y \|$	$\| 5 x + 1 \| = \| 4 x - 9 \|$
$x = + y$ , $+ x = y$	$(5 x + 1) = (4 x - 9)$
$x = - y$ , $- x = y$	$(5 x + 1) = - (4 x - 9)$

2. Solve the two equations for x

7 additional steps

$(5 x + 1) = (4 x - 9)$

Subtract from both sides:

$(5 x + 1) - 4 x = (4 x - 9) - 4 x$

Group like terms:

$(5 x - 4 x) + 1 = (4 x - 9) - 4 x$

Simplify the arithmetic:

$x + 1 = (4 x - 9) - 4 x$

Group like terms:

$x + 1 = (4 x - 4 x) - 9$

Simplify the arithmetic:

$x + 1 = - 9$

Subtract from both sides:

$(x + 1) - 1 = - 9 - 1$

Simplify the arithmetic:

$x = - 9 - 1$

Simplify the arithmetic:

$x = - 10$

10 additional steps

$(5 x + 1) = - (4 x - 9)$

Expand the parentheses:

$(5 x + 1) = - 4 x + 9$

Add to both sides:

$(5 x + 1) + 4 x = (- 4 x + 9) + 4 x$

Group like terms:

$(5 x + 4 x) + 1 = (- 4 x + 9) + 4 x$

Simplify the arithmetic:

$9 x + 1 = (- 4 x + 9) + 4 x$

Group like terms:

$9 x + 1 = (- 4 x + 4 x) + 9$

Simplify the arithmetic:

$9 x + 1 = 9$

Subtract from both sides:

$(9 x + 1) - 1 = 9 - 1$

Simplify the arithmetic:

$9 x = 9 - 1$

Simplify the arithmetic:

$9 x = 8$

Divide both sides by :

$\frac{(9 x)}{9} = \frac{8}{9}$

Simplify the fraction:

$x = \frac{8}{9}$

3. List the solutions

$x = - 10, \frac{8}{9}$
(2 solution(s))

4. Graph

Each line represents the function of one side of the equation:
$y = | 5 x + 1 |$
$y = | 4 x - 9 |$
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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