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Solution - Absolute value equations

Exact form:

r = - \frac{3}{2}

r=-\frac{3}{2}

Mixed number form:

r = - 1 \frac{1}{2}

r=-1\frac{1}{2}

Decimal form:

r = - 1.5

r=-1.5

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
$| 2 r - 4 | = | 2 r + 10 |$
without the absolute value bars:

$\| x \| = \| y \|$	$\| 2 r - 4 \| = \| 2 r + 10 \|$
$x = + y$	$(2 r - 4) = (2 r + 10)$
$x = - y$	$(2 r - 4) = - (2 r + 10)$
$+ x = y$	$(2 r - 4) = (2 r + 10)$
$- x = y$	$- (2 r - 4) = (2 r + 10)$

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:

$\| x \| = \| y \|$	$\| 2 r - 4 \| = \| 2 r + 10 \|$
$x = + y$ , $+ x = y$	$(2 r - 4) = (2 r + 10)$
$x = - y$ , $- x = y$	$(2 r - 4) = - (2 r + 10)$

2. Solve the two equations for r

5 additional steps

$(2 r - 4) = (2 r + 10)$

Subtract from both sides:

$(2 r - 4) - 2 r = (2 r + 10) - 2 r$

Group like terms:

$(2 r - 2 r) - 4 = (2 r + 10) - 2 r$

Simplify the arithmetic:

$- 4 = (2 r + 10) - 2 r$

Group like terms:

$- 4 = (2 r - 2 r) + 10$

Simplify the arithmetic:

$- 4 = 10$

The statement is false:

$- 4 = 10$

The equation is false so it has no solution.

12 additional steps

$(2 r - 4) = - (2 r + 10)$

Expand the parentheses:

$(2 r - 4) = - 2 r - 10$

Add to both sides:

$(2 r - 4) + 2 r = (- 2 r - 10) + 2 r$

Group like terms:

$(2 r + 2 r) - 4 = (- 2 r - 10) + 2 r$

Simplify the arithmetic:

$4 r - 4 = (- 2 r - 10) + 2 r$

Group like terms:

$4 r - 4 = (- 2 r + 2 r) - 10$

Simplify the arithmetic:

$4 r - 4 = - 10$

Add to both sides:

$(4 r - 4) + 4 = - 10 + 4$

Simplify the arithmetic:

$4 r = - 10 + 4$

Simplify the arithmetic:

$4 r = - 6$

Divide both sides by :

$\frac{(4 r)}{4} = \frac{- 6}{4}$

Simplify the fraction:

$r = \frac{- 6}{4}$

Find the greatest common factor of the numerator and denominator:

$r = \frac{(- 3 \cdot 2)}{(2 \cdot 2)}$

Factor out and cancel the greatest common factor:

$r = \frac{- 3}{2}$

3. Graph

Each line represents the function of one side of the equation:
$y = | 2 r - 4 |$
$y = | 2 r + 10 |$
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 r

3. 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 r

3. Graph

Why learn this

Terms and topics

Related links

Latest Related Drills Solved