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Solution - Absolute value equations

Exact form:

r = - 1, \frac{1}{5}

r=-1 , \frac{1}{5}

Decimal form:

r = - 1, 0.2

r=-1 , 0.2

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
$| r - 2 | = | 4 r + 1 |$
without the absolute value bars:

$\| x \| = \| y \|$	$\| r - 2 \| = \| 4 r + 1 \|$
$x = + y$	$(r - 2) = (4 r + 1)$
$x = - y$	$(r - 2) = - (4 r + 1)$
$+ x = y$	$(r - 2) = (4 r + 1)$
$- x = y$	$- (r - 2) = (4 r + 1)$

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:

$\| x \| = \| y \|$	$\| r - 2 \| = \| 4 r + 1 \|$
$x = + y$ , $+ x = y$	$(r - 2) = (4 r + 1)$
$x = - y$ , $- x = y$	$(r - 2) = - (4 r + 1)$

2. Solve the two equations for r

12 additional steps

$(r - 2) = (4 r + 1)$

Subtract from both sides:

$(r - 2) - 4 r = (4 r + 1) - 4 r$

Group like terms:

$(r - 4 r) - 2 = (4 r + 1) - 4 r$

Simplify the arithmetic:

$- 3 r - 2 = (4 r + 1) - 4 r$

Group like terms:

$- 3 r - 2 = (4 r - 4 r) + 1$

Simplify the arithmetic:

$- 3 r - 2 = 1$

Add to both sides:

$(- 3 r - 2) + 2 = 1 + 2$

Simplify the arithmetic:

$- 3 r = 1 + 2$

Simplify the arithmetic:

$- 3 r = 3$

Divide both sides by :

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

Cancel out the negatives:

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

Simplify the fraction:

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

Move the negative sign from the denominator to the numerator:

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

Simplify the fraction:

$r = - 1$

10 additional steps

$(r - 2) = - (4 r + 1)$

Expand the parentheses:

$(r - 2) = - 4 r - 1$

Add to both sides:

$(r - 2) + 4 r = (- 4 r - 1) + 4 r$

Group like terms:

$(r + 4 r) - 2 = (- 4 r - 1) + 4 r$

Simplify the arithmetic:

$5 r - 2 = (- 4 r - 1) + 4 r$

Group like terms:

$5 r - 2 = (- 4 r + 4 r) - 1$

Simplify the arithmetic:

$5 r - 2 = - 1$

Add to both sides:

$(5 r - 2) + 2 = - 1 + 2$

Simplify the arithmetic:

$5 r = - 1 + 2$

Simplify the arithmetic:

$5 r = 1$

Divide both sides by :

$\frac{(5 r)}{5} = \frac{1}{5}$

Simplify the fraction:

$r = \frac{1}{5}$

3. List the solutions

$r = - 1, \frac{1}{5}$
(2 solution(s))

4. Graph

Each line represents the function of one side of the equation:
$y = | r - 2 |$
$y = | 4 r + 1 |$
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 r

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 r

3. List the solutions

4. Graph

Why learn this

Terms and topics

Related links

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