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Solution - Absolute value equations

Exact form:

a = 3

a=3

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
$| - 2 a + 7 | = | - 2 a + 5 |$
without the absolute value bars:

$\| x \| = \| y \|$	$\| - 2 a + 7 \| = \| - 2 a + 5 \|$
$x = + y$	$(- 2 a + 7) = (- 2 a + 5)$
$x = - y$	$(- 2 a + 7) = - (- 2 a + 5)$
$+ x = y$	$(- 2 a + 7) = (- 2 a + 5)$
$- x = y$	$- (- 2 a + 7) = (- 2 a + 5)$

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:

$\| x \| = \| y \|$	$\| - 2 a + 7 \| = \| - 2 a + 5 \|$
$x = + y$ , $+ x = y$	$(- 2 a + 7) = (- 2 a + 5)$
$x = - y$ , $- x = y$	$(- 2 a + 7) = - (- 2 a + 5)$

2. Solve the two equations for a

5 additional steps

$(- 2 a + 7) = (- 2 a + 5)$

Add to both sides:

$(- 2 a + 7) + 2 a = (- 2 a + 5) + 2 a$

Group like terms:

$(- 2 a + 2 a) + 7 = (- 2 a + 5) + 2 a$

Simplify the arithmetic:

$7 = (- 2 a + 5) + 2 a$

Group like terms:

$7 = (- 2 a + 2 a) + 5$

Simplify the arithmetic:

$7 = 5$

The statement is false:

$7 = 5$

The equation is false so it has no solution.

14 additional steps

$(- 2 a + 7) = - (- 2 a + 5)$

Expand the parentheses:

$(- 2 a + 7) = 2 a - 5$

Subtract from both sides:

$(- 2 a + 7) - 2 a = (2 a - 5) - 2 a$

Group like terms:

$(- 2 a - 2 a) + 7 = (2 a - 5) - 2 a$

Simplify the arithmetic:

$- 4 a + 7 = (2 a - 5) - 2 a$

Group like terms:

$- 4 a + 7 = (2 a - 2 a) - 5$

Simplify the arithmetic:

$- 4 a + 7 = - 5$

Subtract from both sides:

$(- 4 a + 7) - 7 = - 5 - 7$

Simplify the arithmetic:

$- 4 a = - 5 - 7$

Simplify the arithmetic:

$- 4 a = - 12$

Divide both sides by :

$\frac{(- 4 a)}{- 4} = \frac{- 12}{- 4}$

Cancel out the negatives:

$\frac{4 a}{4} = \frac{- 12}{- 4}$

Simplify the fraction:

$a = \frac{- 12}{- 4}$

Cancel out the negatives:

$a = \frac{12}{4}$

Find the greatest common factor of the numerator and denominator:

$a = \frac{(3 \cdot 4)}{(1 \cdot 4)}$

Factor out and cancel the greatest common factor:

$a = 3$

3. Graph

Each line represents the function of one side of the equation:
$y = | - 2 a + 7 |$
$y = | - 2 a + 5 |$
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 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