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Solution - Absolute value equations

Exact form:

u = - \frac{3}{2}, 2

u=-\frac{3}{2} , 2

Mixed number form:

u = - 1 \frac{1}{2}, 2

u=-1\frac{1}{2} , 2

Decimal form:

u = - 1.5, 2

u=-1.5 , 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
$| - 3 u - 1 | = | u + 5 |$
without the absolute value bars:

$\| x \| = \| y \|$	$\| - 3 u - 1 \| = \| u + 5 \|$
$x = + y$	$(- 3 u - 1) = (u + 5)$
$x = - y$	$(- 3 u - 1) = - (u + 5)$
$+ x = y$	$(- 3 u - 1) = (u + 5)$
$- x = y$	$- (- 3 u - 1) = (u + 5)$

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:

$\| x \| = \| y \|$	$\| - 3 u - 1 \| = \| u + 5 \|$
$x = + y$ , $+ x = y$	$(- 3 u - 1) = (u + 5)$
$x = - y$ , $- x = y$	$(- 3 u - 1) = - (u + 5)$

2. Solve the two equations for u

13 additional steps

$(- 3 u - 1) = (u + 5)$

Subtract from both sides:

$(- 3 u - 1) - u = (u + 5) - u$

Group like terms:

$(- 3 u - u) - 1 = (u + 5) - u$

Simplify the arithmetic:

$- 4 u - 1 = (u + 5) - u$

Group like terms:

$- 4 u - 1 = (u - u) + 5$

Simplify the arithmetic:

$- 4 u - 1 = 5$

Add to both sides:

$(- 4 u - 1) + 1 = 5 + 1$

Simplify the arithmetic:

$- 4 u = 5 + 1$

Simplify the arithmetic:

$- 4 u = 6$

Divide both sides by :

$\frac{(- 4 u)}{- 4} = \frac{6}{- 4}$

Cancel out the negatives:

$\frac{4 u}{4} = \frac{6}{- 4}$

Simplify the fraction:

$u = \frac{6}{- 4}$

Move the negative sign from the denominator to the numerator:

$u = \frac{- 6}{4}$

Find the greatest common factor of the numerator and denominator:

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

Factor out and cancel the greatest common factor:

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

14 additional steps

$(- 3 u - 1) = - (u + 5)$

Expand the parentheses:

$(- 3 u - 1) = - u - 5$

Add to both sides:

$(- 3 u - 1) + u = (- u - 5) + u$

Group like terms:

$(- 3 u + u) - 1 = (- u - 5) + u$

Simplify the arithmetic:

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

Group like terms:

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

Simplify the arithmetic:

$- 2 u - 1 = - 5$

Add to both sides:

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

Simplify the arithmetic:

$- 2 u = - 5 + 1$

Simplify the arithmetic:

$- 2 u = - 4$

Divide both sides by :

$\frac{(- 2 u)}{- 2} = \frac{- 4}{- 2}$

Cancel out the negatives:

$\frac{2 u}{2} = \frac{- 4}{- 2}$

Simplify the fraction:

$u = \frac{- 4}{- 2}$

Cancel out the negatives:

$u = \frac{4}{2}$

Find the greatest common factor of the numerator and denominator:

$u = \frac{(2 \cdot 2)}{(1 \cdot 2)}$

Factor out and cancel the greatest common factor:

$u = 2$

3. List the solutions

$u = - \frac{3}{2}, 2$
(2 solution(s))

4. Graph

Each line represents the function of one side of the equation:
$y = | - 3 u - 1 |$
$y = | u + 5 |$
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 u

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 u

3. List the solutions

4. Graph

Why learn this

Terms and topics

Related links

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