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Solution - Absolute value equations

Exact form:

a = \frac{7}{2}

a=\frac{7}{2}

Mixed number form:

a = 3 \frac{1}{2}

a=3\frac{1}{2}

Decimal form:

a = 3.5

a=3.5

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
$| a | = | a - 7 |$
without the absolute value bars:

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

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:

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

2. Solve the two equations for a

4 additional steps

$a = (a - 7)$

Subtract from both sides:

$a - a = (a - 7) - a$

Simplify the arithmetic:

$0 = (a - 7) - a$

Group like terms:

$0 = (a - a) - 7$

Simplify the arithmetic:

$0 = - 7$

The statement is false:

$0 = - 7$

The equation is false so it has no solution.

6 additional steps

$a = - (a - 7)$

Expand the parentheses:

$a = - a + 7$

Add to both sides:

$a + a = (- a + 7) + a$

Simplify the arithmetic:

$2 a = (- a + 7) + a$

Group like terms:

$2 a = (- a + a) + 7$

Simplify the arithmetic:

$2 a = 7$

Divide both sides by :

$\frac{(2 a)}{2} = \frac{7}{2}$

Simplify the fraction:

$a = \frac{7}{2}$

3. Graph

Each line represents the function of one side of the equation:
$y = | a |$
$y = | a - 7 |$
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 a

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 a

3. Graph

Why learn this

Terms and topics

Related links

Latest Related Drills Solved