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Solution - Absolute value equations

Exact form:

u = - \frac{11}{4}

u=-\frac{11}{4}

Mixed number form:

u = - 2 \frac{3}{4}

u=-2\frac{3}{4}

Decimal form:

u = - 2.75

u=-2.75

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
$| 2 u + 9 | = | 2 u + 2 |$
without the absolute value bars:

$\| x \| = \| y \|$	$\| 2 u + 9 \| = \| 2 u + 2 \|$
$x = + y$	$(2 u + 9) = (2 u + 2)$
$x = - y$	$(2 u + 9) = - (2 u + 2)$
$+ x = y$	$(2 u + 9) = (2 u + 2)$
$- x = y$	$- (2 u + 9) = (2 u + 2)$

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:

$\| x \| = \| y \|$	$\| 2 u + 9 \| = \| 2 u + 2 \|$
$x = + y$ , $+ x = y$	$(2 u + 9) = (2 u + 2)$
$x = - y$ , $- x = y$	$(2 u + 9) = - (2 u + 2)$

2. Solve the two equations for u

5 additional steps

$(2 u + 9) = (2 u + 2)$

Subtract from both sides:

$(2 u + 9) - 2 u = (2 u + 2) - 2 u$

Group like terms:

$(2 u - 2 u) + 9 = (2 u + 2) - 2 u$

Simplify the arithmetic:

$9 = (2 u + 2) - 2 u$

Group like terms:

$9 = (2 u - 2 u) + 2$

Simplify the arithmetic:

$9 = 2$

The statement is false:

$9 = 2$

The equation is false so it has no solution.

10 additional steps

$(2 u + 9) = - (2 u + 2)$

Expand the parentheses:

$(2 u + 9) = - 2 u - 2$

Add to both sides:

$(2 u + 9) + 2 u = (- 2 u - 2) + 2 u$

Group like terms:

$(2 u + 2 u) + 9 = (- 2 u - 2) + 2 u$

Simplify the arithmetic:

$4 u + 9 = (- 2 u - 2) + 2 u$

Group like terms:

$4 u + 9 = (- 2 u + 2 u) - 2$

Simplify the arithmetic:

$4 u + 9 = - 2$

Subtract from both sides:

$(4 u + 9) - 9 = - 2 - 9$

Simplify the arithmetic:

$4 u = - 2 - 9$

Simplify the arithmetic:

$4 u = - 11$

Divide both sides by :

$\frac{(4 u)}{4} = \frac{- 11}{4}$

Simplify the fraction:

$u = \frac{- 11}{4}$

3. Graph

Each line represents the function of one side of the equation:
$y = | 2 u + 9 |$
$y = | 2 u + 2 |$
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 u

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 u

3. Graph

Why learn this

Terms and topics

Related links

Latest Related Drills Solved