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Solution - Absolute value equations

Exact form:

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

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

Mixed number form:

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

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

Decimal form:

x = 3, - 3.667

x=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
$| x + 7 | = 2 | x + 2 |$
without the absolute value bars:

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

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:

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

2. Solve the two equations for x

12 additional steps

$(x + 7) = 2 \cdot (x + 2)$

Expand the parentheses:

$(x + 7) = 2 x + 2 \cdot 2$

Simplify the arithmetic:

$(x + 7) = 2 x + 4$

Subtract from both sides:

$(x + 7) - 2 x = (2 x + 4) - 2 x$

Group like terms:

$(x - 2 x) + 7 = (2 x + 4) - 2 x$

Simplify the arithmetic:

$- x + 7 = (2 x + 4) - 2 x$

Group like terms:

$- x + 7 = (2 x - 2 x) + 4$

Simplify the arithmetic:

$- x + 7 = 4$

Subtract from both sides:

$(- x + 7) - 7 = 4 - 7$

Simplify the arithmetic:

$- x = 4 - 7$

Simplify the arithmetic:

$- x = - 3$

Multiply both sides by :

$- x \cdot - 1 = - 3 \cdot - 1$

Remove the one(s):

$x = - 3 \cdot - 1$

Simplify the arithmetic:

$x = 3$

14 additional steps

$(x + 7) = 2 \cdot (- (x + 2))$

Expand the parentheses:

$(x + 7) = 2 \cdot (- x - 2)$

$(x + 7) = 2 \cdot - x + 2 \cdot - 2$

Group like terms:

$(x + 7) = (2 \cdot - 1) x + 2 \cdot - 2$

Multiply the coefficients:

$(x + 7) = - 2 x + 2 \cdot - 2$

Simplify the arithmetic:

$(x + 7) = - 2 x - 4$

Add to both sides:

$(x + 7) + 2 x = (- 2 x - 4) + 2 x$

Group like terms:

$(x + 2 x) + 7 = (- 2 x - 4) + 2 x$

Simplify the arithmetic:

$3 x + 7 = (- 2 x - 4) + 2 x$

Group like terms:

$3 x + 7 = (- 2 x + 2 x) - 4$

Simplify the arithmetic:

$3 x + 7 = - 4$

Subtract from both sides:

$(3 x + 7) - 7 = - 4 - 7$

Simplify the arithmetic:

$3 x = - 4 - 7$

Simplify the arithmetic:

$3 x = - 11$

Divide both sides by :

$\frac{(3 x)}{3} = \frac{- 11}{3}$

Simplify the fraction:

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

3. List the solutions

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

4. Graph

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

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 x

3. List the solutions

4. Graph

Why learn this

Terms and topics

Related links

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