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Solution - Absolute value equations

Exact form:

x = \frac{1}{7}, - 9

x=\frac{1}{7} , -9

Decimal form:

x = 0.143, - 9

x=0.143 , -9

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
$| - 3 x + 5 | = 4 | x + 1 |$
without the absolute value bars:

$\| x \| = \| y \|$	$\| - 3 x + 5 \| = 4 \| x + 1 \|$
$x = + y$	$(- 3 x + 5) = 4 (x + 1)$
$x = - y$	$(- 3 x + 5) = 4 (- (x + 1))$
$+ x = y$	$(- 3 x + 5) = 4 (x + 1)$
$- x = y$	$- (- 3 x + 5) = 4 (x + 1)$

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:

$\| x \| = \| y \|$	$\| - 3 x + 5 \| = 4 \| x + 1 \|$
$x = + y$ , $+ x = y$	$(- 3 x + 5) = 4 (x + 1)$
$x = - y$ , $- x = y$	$(- 3 x + 5) = 4 (- (x + 1))$

2. Solve the two equations for x

13 additional steps

$(- 3 x + 5) = 4 \cdot (x + 1)$

Expand the parentheses:

$(- 3 x + 5) = 4 x + 4 \cdot 1$

Simplify the arithmetic:

$(- 3 x + 5) = 4 x + 4$

Subtract from both sides:

$(- 3 x + 5) - 4 x = (4 x + 4) - 4 x$

Group like terms:

$(- 3 x - 4 x) + 5 = (4 x + 4) - 4 x$

Simplify the arithmetic:

$- 7 x + 5 = (4 x + 4) - 4 x$

Group like terms:

$- 7 x + 5 = (4 x - 4 x) + 4$

Simplify the arithmetic:

$- 7 x + 5 = 4$

Subtract from both sides:

$(- 7 x + 5) - 5 = 4 - 5$

Simplify the arithmetic:

$- 7 x = 4 - 5$

Simplify the arithmetic:

$- 7 x = - 1$

Divide both sides by :

$\frac{(- 7 x)}{- 7} = \frac{- 1}{- 7}$

Cancel out the negatives:

$\frac{7 x}{7} = \frac{- 1}{- 7}$

Simplify the fraction:

$x = \frac{- 1}{- 7}$

Cancel out the negatives:

$x = \frac{1}{7}$

12 additional steps

$(- 3 x + 5) = 4 \cdot (- (x + 1))$

Expand the parentheses:

$(- 3 x + 5) = 4 \cdot (- x - 1)$

$(- 3 x + 5) = 4 \cdot - x + 4 \cdot - 1$

Group like terms:

$(- 3 x + 5) = (4 \cdot - 1) x + 4 \cdot - 1$

Multiply the coefficients:

$(- 3 x + 5) = - 4 x + 4 \cdot - 1$

Simplify the arithmetic:

$(- 3 x + 5) = - 4 x - 4$

Add to both sides:

$(- 3 x + 5) + 4 x = (- 4 x - 4) + 4 x$

Group like terms:

$(- 3 x + 4 x) + 5 = (- 4 x - 4) + 4 x$

Simplify the arithmetic:

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

Group like terms:

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

Simplify the arithmetic:

$x + 5 = - 4$

Subtract from both sides:

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

Simplify the arithmetic:

$x = - 4 - 5$

Simplify the arithmetic:

$x = - 9$

3. List the solutions

$x = \frac{1}{7}, - 9$
(2 solution(s))

4. Graph

Each line represents the function of one side of the equation:
$y = | - 3 x + 5 |$
$y = 4 | x + 1 |$
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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