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Solution - Absolute value equations

Exact form:

y = - \frac{3}{2}

y=-\frac{3}{2}

Mixed number form:

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

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

Decimal form:

y = - 1.5

y=-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
$| 3 y + 5 | = | 3 y + 4 |$
without the absolute value bars:

$\| x \| = \| y \|$	$\| 3 y + 5 \| = \| 3 y + 4 \|$
$x = + y$	$(3 y + 5) = (3 y + 4)$
$x = - y$	$(3 y + 5) = - (3 y + 4)$
$+ x = y$	$(3 y + 5) = (3 y + 4)$
$- x = y$	$- (3 y + 5) = (3 y + 4)$

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:

$\| x \| = \| y \|$	$\| 3 y + 5 \| = \| 3 y + 4 \|$
$x = + y$ , $+ x = y$	$(3 y + 5) = (3 y + 4)$
$x = - y$ , $- x = y$	$(3 y + 5) = - (3 y + 4)$

2. Solve the two equations for y

5 additional steps

$(3 y + 5) = (3 y + 4)$

Subtract from both sides:

$(3 y + 5) - 3 y = (3 y + 4) - 3 y$

Group like terms:

$(3 y - 3 y) + 5 = (3 y + 4) - 3 y$

Simplify the arithmetic:

$5 = (3 y + 4) - 3 y$

Group like terms:

$5 = (3 y - 3 y) + 4$

Simplify the arithmetic:

$5 = 4$

The statement is false:

$5 = 4$

The equation is false so it has no solution.

12 additional steps

$(3 y + 5) = - (3 y + 4)$

Expand the parentheses:

$(3 y + 5) = - 3 y - 4$

Add to both sides:

$(3 y + 5) + 3 y = (- 3 y - 4) + 3 y$

Group like terms:

$(3 y + 3 y) + 5 = (- 3 y - 4) + 3 y$

Simplify the arithmetic:

$6 y + 5 = (- 3 y - 4) + 3 y$

Group like terms:

$6 y + 5 = (- 3 y + 3 y) - 4$

Simplify the arithmetic:

$6 y + 5 = - 4$

Subtract from both sides:

$(6 y + 5) - 5 = - 4 - 5$

Simplify the arithmetic:

$6 y = - 4 - 5$

Simplify the arithmetic:

$6 y = - 9$

Divide both sides by :

$\frac{(6 y)}{6} = \frac{- 9}{6}$

Simplify the fraction:

$y = \frac{- 9}{6}$

Find the greatest common factor of the numerator and denominator:

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

Factor out and cancel the greatest common factor:

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

3. Graph

Each line represents the function of one side of the equation:
$y = | 3 y + 5 |$
$y = | 3 y + 4 |$
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. 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. Graph

Why learn this

Terms and topics

Related links

Latest Related Drills Solved