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Solution - Absolute value equations

Exact form:

r = 3, 5

r=3 , 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
$| 2 r - 9 | = | r - 6 |$
without the absolute value bars:

$\| x \| = \| y \|$	$\| 2 r - 9 \| = \| r - 6 \|$
$x = + y$	$(2 r - 9) = (r - 6)$
$x = - y$	$(2 r - 9) = - (r - 6)$
$+ x = y$	$(2 r - 9) = (r - 6)$
$- x = y$	$- (2 r - 9) = (r - 6)$

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:

$\| x \| = \| y \|$	$\| 2 r - 9 \| = \| r - 6 \|$
$x = + y$ , $+ x = y$	$(2 r - 9) = (r - 6)$
$x = - y$ , $- x = y$	$(2 r - 9) = - (r - 6)$

2. Solve the two equations for r

7 additional steps

$(2 r - 9) = (r - 6)$

Subtract from both sides:

$(2 r - 9) - r = (r - 6) - r$

Group like terms:

$(2 r - r) - 9 = (r - 6) - r$

Simplify the arithmetic:

$r - 9 = (r - 6) - r$

Group like terms:

$r - 9 = (r - r) - 6$

Simplify the arithmetic:

$r - 9 = - 6$

Add to both sides:

$(r - 9) + 9 = - 6 + 9$

Simplify the arithmetic:

$r = - 6 + 9$

Simplify the arithmetic:

$r = 3$

12 additional steps

$(2 r - 9) = - (r - 6)$

Expand the parentheses:

$(2 r - 9) = - r + 6$

Add to both sides:

$(2 r - 9) + r = (- r + 6) + r$

Group like terms:

$(2 r + r) - 9 = (- r + 6) + r$

Simplify the arithmetic:

$3 r - 9 = (- r + 6) + r$

Group like terms:

$3 r - 9 = (- r + r) + 6$

Simplify the arithmetic:

$3 r - 9 = 6$

Add to both sides:

$(3 r - 9) + 9 = 6 + 9$

Simplify the arithmetic:

$3 r = 6 + 9$

Simplify the arithmetic:

$3 r = 15$

Divide both sides by :

$\frac{(3 r)}{3} = \frac{15}{3}$

Simplify the fraction:

$r = \frac{15}{3}$

Find the greatest common factor of the numerator and denominator:

$r = \frac{(5 \cdot 3)}{(1 \cdot 3)}$

Factor out and cancel the greatest common factor:

$r = 5$

3. List the solutions

$r = 3, 5$
(2 solution(s))

4. Graph

Each line represents the function of one side of the equation:
$y = | 2 r - 9 |$
$y = | r - 6 |$
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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