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Solution - Absolute value equations

Exact form: x=2,12
x=-2 , -12

Other Ways to Solve

Absolute value equations

Step-by-step explanation

1. Rewrite the equation without absolute value bars

Use the rules:
|x|=|y|x=±y and |x|=|y|±x=y
to write all four options of the equation
|x+3|=|2x+9|
without the absolute value bars:

|x|=|y||x+3|=|2x+9|
x=+y(x+3)=(2x+9)
x=y(x+3)=(2x+9)
+x=y(x+3)=(2x+9)
x=y(x+3)=(2x+9)

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+3|=|2x+9|
x=+y , +x=y(x+3)=(2x+9)
x=y , x=y(x+3)=(2x+9)

2. Solve the two equations for x

13 additional steps

(-x+3)=(2x+9)

Subtract from both sides:

(-x+3)-2x=(2x+9)-2x

Group like terms:

(-x-2x)+3=(2x+9)-2x

Simplify the arithmetic:

-3x+3=(2x+9)-2x

Group like terms:

-3x+3=(2x-2x)+9

Simplify the arithmetic:

3x+3=9

Subtract from both sides:

(-3x+3)-3=9-3

Simplify the arithmetic:

3x=93

Simplify the arithmetic:

3x=6

Divide both sides by :

(-3x)-3=6-3

Cancel out the negatives:

3x3=6-3

Simplify the fraction:

x=6-3

Move the negative sign from the denominator to the numerator:

x=-63

Find the greatest common factor of the numerator and denominator:

x=(-2·3)(1·3)

Factor out and cancel the greatest common factor:

x=2

8 additional steps

(-x+3)=-(2x+9)

Expand the parentheses:

(-x+3)=-2x-9

Add to both sides:

(-x+3)+2x=(-2x-9)+2x

Group like terms:

(-x+2x)+3=(-2x-9)+2x

Simplify the arithmetic:

x+3=(-2x-9)+2x

Group like terms:

x+3=(-2x+2x)-9

Simplify the arithmetic:

x+3=9

Subtract from both sides:

(x+3)-3=-9-3

Simplify the arithmetic:

x=93

Simplify the arithmetic:

x=12

3. List the solutions

x=2,12
(2 solution(s))

4. Graph

Each line represents the function of one side of the equation:
y=|x+3|
y=|2x+9|
The equation is true where the two lines cross.

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.