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Solution - Absolute value equations

Exact form: x=7,3
x=7 , -3

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+8|=|2x+1|
without the absolute value bars:

|x|=|y||x+8|=|2x+1|
x=+y(x+8)=(2x+1)
x=y(x+8)=(2x+1)
+x=y(x+8)=(2x+1)
x=y(x+8)=(2x+1)

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+8|=|2x+1|
x=+y , +x=y(x+8)=(2x+1)
x=y , x=y(x+8)=(2x+1)

2. Solve the two equations for x

10 additional steps

(x+8)=(2x+1)

Subtract from both sides:

(x+8)-2x=(2x+1)-2x

Group like terms:

(x-2x)+8=(2x+1)-2x

Simplify the arithmetic:

-x+8=(2x+1)-2x

Group like terms:

-x+8=(2x-2x)+1

Simplify the arithmetic:

x+8=1

Subtract from both sides:

(-x+8)-8=1-8

Simplify the arithmetic:

x=18

Simplify the arithmetic:

x=7

Multiply both sides by :

-x·-1=-7·-1

Remove the one(s):

x=-7·-1

Simplify the arithmetic:

x=7

12 additional steps

(x+8)=-(2x+1)

Expand the parentheses:

(x+8)=-2x-1

Add to both sides:

(x+8)+2x=(-2x-1)+2x

Group like terms:

(x+2x)+8=(-2x-1)+2x

Simplify the arithmetic:

3x+8=(-2x-1)+2x

Group like terms:

3x+8=(-2x+2x)-1

Simplify the arithmetic:

3x+8=1

Subtract from both sides:

(3x+8)-8=-1-8

Simplify the arithmetic:

3x=18

Simplify the arithmetic:

3x=9

Divide both sides by :

(3x)3=-93

Simplify the fraction:

x=-93

Find the greatest common factor of the numerator and denominator:

x=(-3·3)(1·3)

Factor out and cancel the greatest common factor:

x=3

3. List the solutions

x=7,3
(2 solution(s))

4. Graph

Each line represents the function of one side of the equation:
y=|x+8|
y=|2x+1|
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.