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Solution - Absolute value equations

Exact form:

y = \frac{9}{2}, - 9

y=\frac{9}{2} , -9

Mixed number form:

y = 4 \frac{1}{2}, - 9

y=4\frac{1}{2} , -9

Decimal form:

y = 4.5, - 9

y=4.5 , -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
$| 2 y - 9 | = | - 2 y + 9 |$
without the absolute value bars:

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

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:

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

2. Solve the two equations for y

11 additional steps

$(2 y - 9) = (- 2 y + 9)$

Add to both sides:

$(2 y - 9) + 2 y = (- 2 y + 9) + 2 y$

Group like terms:

$(2 y + 2 y) - 9 = (- 2 y + 9) + 2 y$

Simplify the arithmetic:

$4 y - 9 = (- 2 y + 9) + 2 y$

Group like terms:

$4 y - 9 = (- 2 y + 2 y) + 9$

Simplify the arithmetic:

$4 y - 9 = 9$

Add to both sides:

$(4 y - 9) + 9 = 9 + 9$

Simplify the arithmetic:

$4 y = 9 + 9$

Simplify the arithmetic:

$4 y = 18$

Divide both sides by :

$\frac{(4 y)}{4} = \frac{18}{4}$

Simplify the fraction:

$y = \frac{18}{4}$

Find the greatest common factor of the numerator and denominator:

$y = \frac{(9 \cdot 2)}{(2 \cdot 2)}$

Factor out and cancel the greatest common factor:

$y = \frac{9}{2}$

5 additional steps

$(2 y - 9) = - (- 2 y + 9)$

Expand the parentheses:

$(2 y - 9) = 2 y - 9$

Subtract from both sides:

$(2 y - 9) - 2 y = (2 y - 9) - 2 y$

Group like terms:

$(2 y - 2 y) - 9 = (2 y - 9) - 2 y$

Simplify the arithmetic:

$- 9 = (2 y - 9) - 2 y$

Group like terms:

$- 9 = (2 y - 2 y) - 9$

Simplify the arithmetic:

$- 9 = - 9$

3. List the solutions

$y = \frac{9}{2}, - 9$
(2 solution(s))

4. Graph

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

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 y

3. List the solutions

4. Graph

Why learn this

Terms and topics

Related links

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