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Solution - Absolute value equations

Exact form:

y = 3, 9

y=3 , 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
$| 2 y - 3 | = | - 3 y + 12 |$
without the absolute value bars:

$\| x \| = \| y \|$	$\| 2 y - 3 \| = \| - 3 y + 12 \|$
$x = + y$	$(2 y - 3) = (- 3 y + 12)$
$x = - y$	$(2 y - 3) = - (- 3 y + 12)$
$+ x = y$	$(2 y - 3) = (- 3 y + 12)$
$- x = y$	$- (2 y - 3) = (- 3 y + 12)$

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:

$\| x \| = \| y \|$	$\| 2 y - 3 \| = \| - 3 y + 12 \|$
$x = + y$ , $+ x = y$	$(2 y - 3) = (- 3 y + 12)$
$x = - y$ , $- x = y$	$(2 y - 3) = - (- 3 y + 12)$

2. Solve the two equations for y

11 additional steps

$(2 y - 3) = (- 3 y + 12)$

Add to both sides:

$(2 y - 3) + 3 y = (- 3 y + 12) + 3 y$

Group like terms:

$(2 y + 3 y) - 3 = (- 3 y + 12) + 3 y$

Simplify the arithmetic:

$5 y - 3 = (- 3 y + 12) + 3 y$

Group like terms:

$5 y - 3 = (- 3 y + 3 y) + 12$

Simplify the arithmetic:

$5 y - 3 = 12$

Add to both sides:

$(5 y - 3) + 3 = 12 + 3$

Simplify the arithmetic:

$5 y = 12 + 3$

Simplify the arithmetic:

$5 y = 15$

Divide both sides by :

$\frac{(5 y)}{5} = \frac{15}{5}$

Simplify the fraction:

$y = \frac{15}{5}$

Find the greatest common factor of the numerator and denominator:

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

Factor out and cancel the greatest common factor:

$y = 3$

11 additional steps

$(2 y - 3) = - (- 3 y + 12)$

Expand the parentheses:

$(2 y - 3) = 3 y - 12$

Subtract from both sides:

$(2 y - 3) - 3 y = (3 y - 12) - 3 y$

Group like terms:

$(2 y - 3 y) - 3 = (3 y - 12) - 3 y$

Simplify the arithmetic:

$- y - 3 = (3 y - 12) - 3 y$

Group like terms:

$- y - 3 = (3 y - 3 y) - 12$

Simplify the arithmetic:

$- y - 3 = - 12$

Add to both sides:

$(- y - 3) + 3 = - 12 + 3$

Simplify the arithmetic:

$- y = - 12 + 3$

Simplify the arithmetic:

$- y = - 9$

Multiply both sides by :

$- y \cdot - 1 = - 9 \cdot - 1$

Remove the one(s):

$y = - 9 \cdot - 1$

Simplify the arithmetic:

$y = 9$

3. List the solutions

$y = 3, 9$
(2 solution(s))

4. Graph

Each line represents the function of one side of the equation:
$y = | 2 y - 3 |$
$y = | - 3 y + 12 |$
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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