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Solution - Absolute value equations

Exact form:

a = \frac{8}{5}

a=\frac{8}{5}

Mixed number form:

a = 1 \frac{3}{5}

a=1\frac{3}{5}

Decimal form:

a = 1.6

a=1.6

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
$| - 5 a + 9 | = | - 5 a + 7 |$
without the absolute value bars:

$\| x \| = \| y \|$	$\| - 5 a + 9 \| = \| - 5 a + 7 \|$
$x = + y$	$(- 5 a + 9) = (- 5 a + 7)$
$x = - y$	$(- 5 a + 9) = - (- 5 a + 7)$
$+ x = y$	$(- 5 a + 9) = (- 5 a + 7)$
$- x = y$	$- (- 5 a + 9) = (- 5 a + 7)$

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:

$\| x \| = \| y \|$	$\| - 5 a + 9 \| = \| - 5 a + 7 \|$
$x = + y$ , $+ x = y$	$(- 5 a + 9) = (- 5 a + 7)$
$x = - y$ , $- x = y$	$(- 5 a + 9) = - (- 5 a + 7)$

2. Solve the two equations for a

5 additional steps

$(- 5 a + 9) = (- 5 a + 7)$

Add to both sides:

$(- 5 a + 9) + 5 a = (- 5 a + 7) + 5 a$

Group like terms:

$(- 5 a + 5 a) + 9 = (- 5 a + 7) + 5 a$

Simplify the arithmetic:

$9 = (- 5 a + 7) + 5 a$

Group like terms:

$9 = (- 5 a + 5 a) + 7$

Simplify the arithmetic:

$9 = 7$

The statement is false:

$9 = 7$

The equation is false so it has no solution.

14 additional steps

$(- 5 a + 9) = - (- 5 a + 7)$

Expand the parentheses:

$(- 5 a + 9) = 5 a - 7$

Subtract from both sides:

$(- 5 a + 9) - 5 a = (5 a - 7) - 5 a$

Group like terms:

$(- 5 a - 5 a) + 9 = (5 a - 7) - 5 a$

Simplify the arithmetic:

$- 10 a + 9 = (5 a - 7) - 5 a$

Group like terms:

$- 10 a + 9 = (5 a - 5 a) - 7$

Simplify the arithmetic:

$- 10 a + 9 = - 7$

Subtract from both sides:

$(- 10 a + 9) - 9 = - 7 - 9$

Simplify the arithmetic:

$- 10 a = - 7 - 9$

Simplify the arithmetic:

$- 10 a = - 16$

Divide both sides by :

$\frac{(- 10 a)}{- 10} = \frac{- 16}{- 10}$

Cancel out the negatives:

$\frac{10 a}{10} = \frac{- 16}{- 10}$

Simplify the fraction:

$a = \frac{- 16}{- 10}$

Cancel out the negatives:

$a = \frac{16}{10}$

Find the greatest common factor of the numerator and denominator:

$a = \frac{(8 \cdot 2)}{(5 \cdot 2)}$

Factor out and cancel the greatest common factor:

$a = \frac{8}{5}$

3. Graph

Each line represents the function of one side of the equation:
$y = | - 5 a + 9 |$
$y = | - 5 a + 7 |$
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