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Solution - Absolute value equations

Exact form:

x = \frac{3}{4}, - \frac{1}{2}

x=\frac{3}{4} , -\frac{1}{2}

Decimal form:

x = 0.75, - 0.5

x=0.75 , -0.5

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
$| 3 x + 4 | = | 7 x + 1 |$
without the absolute value bars:

$\| x \| = \| y \|$	$\| 3 x + 4 \| = \| 7 x + 1 \|$
$x = + y$	$(3 x + 4) = (7 x + 1)$
$x = - y$	$(3 x + 4) = - (7 x + 1)$
$+ x = y$	$(3 x + 4) = (7 x + 1)$
$- x = y$	$- (3 x + 4) = (7 x + 1)$

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:

$\| x \| = \| y \|$	$\| 3 x + 4 \| = \| 7 x + 1 \|$
$x = + y$ , $+ x = y$	$(3 x + 4) = (7 x + 1)$
$x = - y$ , $- x = y$	$(3 x + 4) = - (7 x + 1)$

2. Solve the two equations for x

11 additional steps

$(3 x + 4) = (7 x + 1)$

Subtract from both sides:

$(3 x + 4) - 7 x = (7 x + 1) - 7 x$

Group like terms:

$(3 x - 7 x) + 4 = (7 x + 1) - 7 x$

Simplify the arithmetic:

$- 4 x + 4 = (7 x + 1) - 7 x$

Group like terms:

$- 4 x + 4 = (7 x - 7 x) + 1$

Simplify the arithmetic:

$- 4 x + 4 = 1$

Subtract from both sides:

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

Simplify the arithmetic:

$- 4 x = 1 - 4$

Simplify the arithmetic:

$- 4 x = - 3$

Divide both sides by :

$\frac{(- 4 x)}{- 4} = \frac{- 3}{- 4}$

Cancel out the negatives:

$\frac{4 x}{4} = \frac{- 3}{- 4}$

Simplify the fraction:

$x = \frac{- 3}{- 4}$

Cancel out the negatives:

$x = \frac{3}{4}$

12 additional steps

$(3 x + 4) = - (7 x + 1)$

Expand the parentheses:

$(3 x + 4) = - 7 x - 1$

Add to both sides:

$(3 x + 4) + 7 x = (- 7 x - 1) + 7 x$

Group like terms:

$(3 x + 7 x) + 4 = (- 7 x - 1) + 7 x$

Simplify the arithmetic:

$10 x + 4 = (- 7 x - 1) + 7 x$

Group like terms:

$10 x + 4 = (- 7 x + 7 x) - 1$

Simplify the arithmetic:

$10 x + 4 = - 1$

Subtract from both sides:

$(10 x + 4) - 4 = - 1 - 4$

Simplify the arithmetic:

$10 x = - 1 - 4$

Simplify the arithmetic:

$10 x = - 5$

Divide both sides by :

$\frac{(10 x)}{10} = \frac{- 5}{10}$

Simplify the fraction:

$x = \frac{- 5}{10}$

Find the greatest common factor of the numerator and denominator:

$x = \frac{(- 1 \cdot 5)}{(2 \cdot 5)}$

Factor out and cancel the greatest common factor:

$x = \frac{- 1}{2}$

3. List the solutions

$x = \frac{3}{4}, - \frac{1}{2}$
(2 solution(s))

4. Graph

Each line represents the function of one side of the equation:
$y = | 3 x + 4 |$
$y = | 7 x + 1 |$
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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