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Solution - Absolute value equations

Exact form:

k = 3, - \frac{11}{3}

k=3 , -\frac{11}{3}

Mixed number form:

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

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

Decimal form:

k = 3, - 3.667

k=3 , -3.667

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
$2 | k + 7 | = | 4 k + 8 |$
without the absolute value bars:

$\| x \| = \| y \|$	$2 \| k + 7 \| = \| 4 k + 8 \|$
$x = + y$	$2 (k + 7) = (4 k + 8)$
$x = - y$	$2 (k + 7) = - (4 k + 8)$
$+ x = y$	$2 (k + 7) = (4 k + 8)$
$- x = y$	$2 (- (k + 7)) = (4 k + 8)$

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:

$\| x \| = \| y \|$	$2 \| k + 7 \| = \| 4 k + 8 \|$
$x = + y$ , $+ x = y$	$2 (k + 7) = (4 k + 8)$
$x = - y$ , $- x = y$	$2 (k + 7) = - (4 k + 8)$

2. Solve the two equations for k

15 additional steps

$2 \cdot (k + 7) = (4 k + 8)$

Expand the parentheses:

$2 k + 2 \cdot 7 = (4 k + 8)$

Simplify the arithmetic:

$2 k + 14 = (4 k + 8)$

Subtract from both sides:

$(2 k + 14) - 4 k = (4 k + 8) - 4 k$

Group like terms:

$(2 k - 4 k) + 14 = (4 k + 8) - 4 k$

Simplify the arithmetic:

$- 2 k + 14 = (4 k + 8) - 4 k$

Group like terms:

$- 2 k + 14 = (4 k - 4 k) + 8$

Simplify the arithmetic:

$- 2 k + 14 = 8$

Subtract from both sides:

$(- 2 k + 14) - 14 = 8 - 14$

Simplify the arithmetic:

$- 2 k = 8 - 14$

Simplify the arithmetic:

$- 2 k = - 6$

Divide both sides by :

$\frac{(- 2 k)}{- 2} = \frac{- 6}{- 2}$

Cancel out the negatives:

$\frac{2 k}{2} = \frac{- 6}{- 2}$

Simplify the fraction:

$k = \frac{- 6}{- 2}$

Cancel out the negatives:

$k = \frac{6}{2}$

Find the greatest common factor of the numerator and denominator:

$k = \frac{(3 \cdot 2)}{(1 \cdot 2)}$

Factor out and cancel the greatest common factor:

$k = 3$

14 additional steps

$2 \cdot (k + 7) = - (4 k + 8)$

Expand the parentheses:

$2 k + 2 \cdot 7 = - (4 k + 8)$

Simplify the arithmetic:

$2 k + 14 = - (4 k + 8)$

Expand the parentheses:

$2 k + 14 = - 4 k - 8$

Add to both sides:

$(2 k + 14) + 4 k = (- 4 k - 8) + 4 k$

Group like terms:

$(2 k + 4 k) + 14 = (- 4 k - 8) + 4 k$

Simplify the arithmetic:

$6 k + 14 = (- 4 k - 8) + 4 k$

Group like terms:

$6 k + 14 = (- 4 k + 4 k) - 8$

Simplify the arithmetic:

$6 k + 14 = - 8$

Subtract from both sides:

$(6 k + 14) - 14 = - 8 - 14$

Simplify the arithmetic:

$6 k = - 8 - 14$

Simplify the arithmetic:

$6 k = - 22$

Divide both sides by :

$\frac{(6 k)}{6} = \frac{- 22}{6}$

Simplify the fraction:

$k = \frac{- 22}{6}$

Find the greatest common factor of the numerator and denominator:

$k = \frac{(- 11 \cdot 2)}{(3 \cdot 2)}$

Factor out and cancel the greatest common factor:

$k = \frac{- 11}{3}$

3. List the solutions

$k = 3, - \frac{11}{3}$
(2 solution(s))

4. Graph

Each line represents the function of one side of the equation:
$y = 2 | k + 7 |$
$y = | 4 k + 8 |$
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 k

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 k

3. List the solutions

4. Graph

Why learn this

Terms and topics

Related links

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